Chemical evidence of the changes of the Antarctic Bottom Water ventilation in the western Ross Sea between 1997 and 2003

NASA Astrophysics Data System (ADS)

Rivaro, Paola; Massolo, Serena; Bergamasco, Andrea; Castagno, Pasquale; Budillon, Giorgio

2010-05-01

Data from three Italian CLIMA project cruises between 1997 and 2003 were used to obtain sections of the hydrographic and chemical properties of the main water masses across the shelf break off Cape Adare (western Ross Sea, Antarctica). Dissolved oxygen, nitrate and phosphate data were combined on the basis of the Redfield ratio to obtain the quasi-conservative tracers NO (9[NO 3]+[O 2]), PO (135[PO 4]+[O 2]) and phosphate star PO4* ( PO4*=[PO 4]+[O 2]/175-1.95). In 1997 and 2003 the presence of the High Salinity Shelf Water at the bottom depth near the sill was traced by both physical and chemical measurements. In 2001 the Modified Shelf Water, characterized by warmer temperature and by a lower dissolved oxygen content than High Salinity Shelf Water, was observed at the shelf edge. The distribution of the chemical tracers together with the hydrographic observations showed recently formed Antarctic Bottom Water on the continental slope during all of the cruises. These observations were confirmed by the extended optimum multiparameter analysis. The calculated thickness of the new Antarctic Bottom Water, as well as the tracer content, were variable in time and in space. The estimated volume of the new Antarctic Bottom Water and the export of dissolved oxygen and nutrient associated with the overflowing water were different over the examined period. In particular, a lower (˜55%) export was evidenced in 2001 compared to 1997.

Water masses transform at mid-depths over the Antarctic Continental Slope

NASA Astrophysics Data System (ADS)

Mead Silvester, Jess; Lenn, Yueng-Djern; Polton, Jeffrey; Phillips, Helen E.; Morales Maqueda, Miguel

2017-04-01

The Meridional Overturning Circulation (MOC) controls the oceans' latitudinal heat distribution, helping to regulate the Earth's climate. The Southern Ocean is the primary place where cool, deep waters return to the surface to complete this global circulation. While water mass transformations intrinsic to this process predominantly take place at the surface following upwelling, recent studies implicate vertical mixing in allowing transformation at mid-depths over the Antarctic continental slope. We deployed an EM-Apex float near Elephant Island, north of the Antarctic Peninsula's tip, to profile along the slope and use potential vorticity to diagnose observed instabilities. The float captures direct heat exchange between a lens of Upper Circumpolar Deep Water (UCDW) and surrounding Lower Circumpolar Deep Waters (LCDW) at mid-depths and over the course of several days. Heat fluxes peak across the top and bottom boundaries of the UCDW lens and peak diffusivities across the bottom boundary are associated with shear instability. Estimates of diffusivity from shear-strain finestructure parameterisation and heat fluxes are found to be in reasonable agreement. The two-dimensional Ertel potential vorticity is elevated both inside the UCDW lens and along its bottom boundary, with a strong contribution from the shear term in these regions and instabilities are associated with gravitational and symmetric forcing. Thus, shear instabilities are driving turbulent mixing across the lower boundary between these two water masses, leading to the observed heat exchange and transformation at mid-depths over the Antarctic continental slope. This has implications for our understanding of the rates of upwelling and ocean-atmosphere exchanges of heat and carbon at this critical location.

TUBEWALL: a passive solar thermo-siphoning, field-fabricated, water storage wall system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, F.; Hemker, P.

1980-01-01

The basic component of TUBEWALL is a water-filled thin-wall cylindrical tube with an insulating foam vertical partition insert that divides the inside of the tube into a thin collector water compartment (solar side) and a larger storage water compartment (room side). The two compartments are connected at the top and bottom by means of circulation holes in the foam partition. When the sun strikes the solar side of the tube, the thin layer of collector water is heated, thermosiphons through the top opening in the partition into the larger storage compartment on the room side, and is replaced with coolmore » water drawn from the bottom of the storage through the bottom hole in the partition. Night back-siphonage is prevented by a thin flap valve over the top circulation hole. The tubes may by used between wall studs having a low-cost fiberglass/tedlar double glazing. The tubes can be covered on the room side with drywall and heat transferred to the living space by indirect radiation, and either natural air convection through top and bottom vent slots or by fan. Alternatively, the tubes can be left exposed for direct radiation.« less

Near bottom temperature anomalies in the Dead Sea

NASA Astrophysics Data System (ADS)

Ben-Avraham, Zvi; Ballard, Robert D.

1984-12-01

A bottom photographic and temperature study was carried out in the Dead Sea using a miniature version of the unmanned camera system ANGUS (mini-ANGUS). Due to the low transparency of the Dead Sea water, the bottom photographs provide very poor results. Only in a very few locations was the floor visible and in those cases it was found to be a white undulating sedimentary surface. The bottom temperature measurements, which were made continuously along the ship track, indicate the presence of a large zone of temperature anomalies. This zone is located in the deep part of the north basin at a water depth of over 330 m. The anomalies occur above a portion of an east-west fault which cuts through the Dead Sea suggesting the presence of hydrothermal activity.

A Hydrographic and CFC Survey on the Adelie Land Shelf

NASA Astrophysics Data System (ADS)

Warner, M. J.; Rintoul, S. R.; Tilbrook, B.; Bullister, J. L.; Sonnerup, R. E.

2008-12-01

During 16 Dec 07 - 27 Jan 08, a hydrographic survey of the Antarctic shelf adjacent to Adelie Land was carried out as part of the joint Australian programs - Climate of Antarctica and the Southern Ocean (CASO) and Collaborative East Antarctic Marine Census (CEAMARC) - from aboard the RSV Aurora Australis. Over 80 CTD stations were occupied on the shelf or adjacent slope in the region between 139° 13' E and 145° E. In addition to hydrographic parameters, dissolved oxygen and nutrients, CFCs, dissolved inorganic carbon, and total alkalinity were measured at nearly all of these stations. Several features of the CFC distributions stand out in this formation region of Adelie Land Bottom Water (ALBW) and appear to be related to the bathymetry of the shelf. There are two depressions in this region, both deeper than 800 m - one on the western edge of the study region and the other adjacent to the Mertz Glacial Tongue on the eastern side of the study region. Throughout most of the study area, the presence of Highly-Modified Circumpolar Deep Water (HMCDW) is reflected in mid-depth CFC concentration minima. However, HMCDW is not present in the shallower region between the depressions. Beneath the HMCDW, CFC concentrations generally increase towards the seafloor. The bottom water CFC concentrations below 600 m in the easternmost of these basins are 5-10% higher than those of the westernmost depression. The bottom water dissolved oxygen concentrations are also higher by approximately 15 μmol kg-1 in bottom waters of the eastern depression. The circulation in the eastern depression is cyclonic and bottom waters can flow out of the basin through a trough in the shelf break near 143° E. Waters with high CFC concentrations were detected on the downslope side of the trough - indicating that ALBW was being supplied to the deep Australia-Antarctic Basin even during summer. The data from this expedition will be compared to previous CFC measurements from this region over the past decade.

25. Typical valves used to control flow into and out ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

25. Typical valves used to control flow into and out of filtration bed. Left valve (painted red) drains the bed, and center valve (painted green) admits water into the bed. The right valve is a cross over valve which is used to admit water into a dry bed from the bottom. This bottom fill excludes entrapped air as the bed is filled. When the water reached to top of the bed, filling is continued from the top of the bed. - Lake Whitney Water Filtration Plant, Filtration Plant, South side of Armory Street between Edgehill Road & Whitney Avenue, Hamden, New Haven County, CT

Fishing and bottom water temperature as drivers of change in maximum shell length in Atlantic surfclams (Spisula solidissima)

NASA Astrophysics Data System (ADS)

Munroe, D. M.; Narváez, D. A.; Hennen, D.; Jacobson, L.; Mann, R.; Hofmann, E. E.; Powell, E. N.; Klinck, J. M.

2016-03-01

Maximum shell length of Atlantic surfclams (Spisula solidissima) on the Middle Atlantic Bight (MAB) continental shelf, obtained from federal fishery survey data from 1982-present, has decreased by 15-20 mm. Two potential causes of this decreasing trend, fishery removal of large animals and stress due to warming bottom temperatures, were investigated using an individual-based model for post-settlement surfclams and a fifty-year hindcast of bottom water temperatures on the MAB. Simulations showed that fishing and/or warming bottom water temperature can cause decreases in maximum surfclam shell length (body size) equivalent to those observed in the fished stock. Independently, either localized fishing rates of 20% or sustained bottom temperatures that are 2 °C warmer than average conditions generate the observed decrease in maximum shell length. However, these independent conditions represent extremes and are not sustained in the MAB. The combined effects of fishing and warmer temperatures can generate simulated length decreases that are similar to observed decreases. Interannual variability in bottom water temperatures can also generate fluctuations in simulated shell length of up to 20 mm over a period of 10-15 years. If the change in maximum size is not genotypic, simulations also suggest that shell size composition of surfclam populations can recover if conditions change; however, that recovery could take a decade to become evident.

Enrichment of stream water with fecal indicator organisms from bottom sediments during baseflow periods

USDA-ARS?s Scientific Manuscript database

Fecal indicator organisms (FIOs) are generally believed to be present in surface waters due solely to direct deposition of feces or through transport in runoff. However, emerging evidence points toward hyporheic exchange between sediment pore water and the overlying water column during baseflow peri...

19. EMPTY SEDIMENTATION TANKS. TOP LAYER OF WATER FLOWS OVER ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

19. EMPTY SEDIMENTATION TANKS. TOP LAYER OF WATER FLOWS OVER TRIANGULATED CHANNELS AND OUT THE RAISED DUCTS TO FILTRATION PLANT. MOVEABLE BOARDS ON BOTTOM ASSIST IN REMOVING SLUDGE. VIEW LOOKING NORTHEAST. FILTER CONTROL BUILDING AT REAR. - F. E. Weymouth Filtration Plant, 700 North Moreno Avenue, La Verne, Los Angeles County, CA

Bathymetric analysis of in-water upwelling-radiance data

NASA Astrophysics Data System (ADS)

Fay, Temple H.; Miller, H. V.; Clark, R. K.

1990-09-01

In June 1988, the Naval Ocean Research and Development Activity (NORDA) collected some "in-water" data using its Towed Underwater Pumping System (TUPS) in the near-shore waters off St. Andrews State Park, Shell Island, Florida. These in situ data include latitude; longitude; depth in meters; narrow-band upwelling at 465 nm, 507 nm, and 532 nm; broad-band downwelling collected at the surface; temperature; salinity; atid transmissivity. In this paper, we investigate the relationship between depth and the normalized upwelling irradiance (upwelling divided by downwelling) in the three bands. Algorithms used to calculate water depth from remotely sensed airborne and satellite multispectral data are applied to the TUPS data and results compared. The TEJPS data have the advantage over most aircraft- and satellite-collected data because they were collected over an essentially uniform bottom type (smooth sandy bottom with steady slope) and have no atmospheric contamination. A new algorithm for depth calculation is proposed.

Deep inflow into the Mozambique Basin

NASA Astrophysics Data System (ADS)

Read, J. F.; Pollard, R. T.

1999-02-01

More than 200 conductivity-temperature-depth (CTD) stations were worked around the Southwest Indian Ridge and Del Caño Rise as part of the World Ocean Circulation Experiment. A selection of these data provides information about the inflow of bottom water into the Mozambique Basin. The basin is closed below 3000 m, yet the inflow is significantly large, of order 1 Sv (1 Sv = 106 m3 s-1). Estimates of the basin-scale upwelling at 4000 m suggest that the vertical velocity is also large, 10 × 10-5 cm s-1 or more, an order of magnitude greater than global ocean estimates. Examination of the characteristics of the bottom water in the Mozambique and Agulhas Basins and the Prince Edward Fracture Zone shows that bottom water enters the Mozambique Basin from the Agulhas Basin and also directly from the Enderby Basin. Most of the transport enters the Mozambique Basin via the Agulhas Basin, where two regions of northward flow below 4000 m are found. The major flow, on the eastern flank of the Mozambique Ridge, is through and above the deep, extending (5900 m) trench that connects the Agulhas and Mozambique Basins. The second, weaker flow enters the Transkei Basin along the deep eastern flank of the Agulhas Plateau, then turning east into the Mozambique Basin. The only source of bottom water to the Agulhas Basin is the Enderby Basin, but a more direct route between the Enderby and Mozambique Basins exists via the Prince Edward fracture, which extends deeper than 4000 m throughout its length and links the two basins directly across the Southwest Indian Ridge. Full depth CTD stations trace the changing characteristics of the deep and bottom water in the fracture, and moored current meter data show the strength and persistence of the throughflow. Strong mixing with the overlying deep water elevates the salt content of the bottom water by comparison with the other water in the Mozambique Basin. Thus two distinct bottom waters of the Mozambique Basin originate in the same place (the Enderby Basin), and their different characteristics are solely a function of the routes they have taken and the processes encountered along the different pathways.

Assessing the quality of bottom water temperatures from the Finite-Volume Community Ocean Model (FVCOM) in the Northwest Atlantic Shelf region

NASA Astrophysics Data System (ADS)

Li, Bai; Tanaka, Kisei R.; Chen, Yong; Brady, Damian C.; Thomas, Andrew C.

2017-09-01

The Finite-Volume Community Ocean Model (FVCOM) is an advanced coastal circulation model widely utilized for its ability to simulate spatially and temporally evolving three-dimensional geophysical conditions of complex and dynamic coastal regions. While a body of literature evaluates model skill in surface fields, independent studies validating model skill in bottom fields over large spatial and temporal scales are scarce because these fields cannot be remotely sensed. In this study, an evaluation of FVCOM skill in modeling bottom water temperature was conducted by comparison to hourly in situ observed bottom temperatures recorded by the Environmental Monitors on Lobster Traps (eMOLT), a program that attached thermistors to commercial lobster traps from 2001 to 2013. Over 2 × 106 pairs of FVCOM-eMOLT records were evaluated by a series of statistical measures to quantify accuracy and precision of the modeled data across the Northwest Atlantic Shelf region. The overall comparison between modeled and observed data indicates reliable skill of FVCOM (r2 = 0.72; root mean squared error = 2.28 °C). Seasonally, the average absolute errors show higher model skill in spring, fall and winter than summer. We speculate that this is due to the increased difficulty of modeling high frequency variability in the exact position of the thermocline and frontal zones. The spatial patterns of the residuals suggest that there is improved similarity between modeled and observed data at higher latitudes. We speculate that this is due to increased tidal mixing at higher latitudes in our study area that reduces stratification in winter, allowing improved model accuracy. Modeled bottom water temperatures around Cape Cod, the continental shelf edges, and at one location at the entrance to Penobscot Bay were characterized by relatively high errors. Constraints for future uses of FVCOM bottom water temperature are provided based on the uncertainties in temporal-spatial patterns. This study is novel as it is the first skill assessment of a regional ocean circulation model in bottom fields at high spatial and temporal scales in the Northwest Atlantic Shelf region.

Hyperspectral signatures and WorldView-3 imagery of Indian River Lagoon and Banana River Estuarine water and bottom types

NASA Astrophysics Data System (ADS)

Bostater, Charles R.; Oney, Taylor S.; Rotkiske, Tyler; Aziz, Samin; Morrisette, Charles; Callahan, Kelby; Mcallister, Devin

2017-10-01

Hyperspectral signatures and imagery collected during the spring and summer of 2017 and 2016 are presented. Ground sampling distances (GSD) and pixel sizes were sampled from just over a meter to less than 4.0 mm. A pushbroom hyperspectral imager was used to calculate bidirectional reflectance factor (BRF) signatures. Hyperspectral signatures of different water types and bottom habitats such as submerged seagrasses, drift algae and algal bloom waters were scanned using a high spectral and digital resolution solid state spectrograph. WorldView-3 satellite imagery with minimal water wave sun glint effects was used to demonstrate the ability to detect bottom features using a derivative reflectance spectroscopy approach with the 1.3 m GSD multispectral satellite channels centered at the solar induced fluorescence band. The hyperspectral remote sensing data collected from the Banana River and Indian River Lagoon watersheds represents previously unknown signatures to be used in satellite and airborne remote sensing of water in turbid waters along the US Atlantic Ocean coastal region and the Florida littoral zone.

Peculiarities of spreading of acoustic waves over a shelf with decreasing depth

NASA Astrophysics Data System (ADS)

Dolgikh, G. I.; Budrin, S. S.; Ovcharenko, V. V.; Plotnikov, A. A.

2016-09-01

We analyze experimental data collected in Vityaz Bay of the Sea of Japan during study of the peculiarities of spreading of hydroacoustic waves over a shelf with decreasing depth. We found that the waves propagate over a shelf with depths greater than half of the hydroacoustic wave according to the law of cylindrical divergence with least losses of the wave energy. If the depths are shallower than half of the hydroacoustic wave, they spread along the water-bottom boundary as Rayleigh waves of decaying and undamped types with significant absorption of the wave energy by the bottom.

MODELING SEDIMENT-NUTRIENT FLUX AND SEDIMENT OXYGEN DEMAND

EPA Science Inventory

Depositional flux of particulate organic matter in bottom sediments affects nutrients cycling at the sediment-water interface and consumes oxygen from the overlying water in streams, lakes, and estuaries. This project deals with analytical modeling of nitrogen and carbon producti...

Mixing on the Heard Island Plateau during HEOBI

NASA Astrophysics Data System (ADS)

Robertson, R.

2016-12-01

On the plateau near Heard and McDonald Islands, the water column was nearly always well mixed. Typically, temperature differences between the surface and the bottom, 100-200 m, were less than 0.2oC and often less that 0.1oC. Surface stratification developed through insolation and deep primarily through a combination of upwelling from canyons and over the edge of the plateau and tidal advection. This stratification was primarily removed by a combination of wind and tidal mixing. Persistent winds of 30 knots mixed the upper 20-50 m. Strong wind events, 40-60 knots, mixed the water column to 100-200 m depth, which over the plateau, was often the entire water column. Benthic tidal friction mixed the bottom 30-50 m. Although the water column was unstratified at the two plume sites intensively investigated, tidal velocities were baroclinic, probably due to topographic controls. Tidal advection changed the bottom temperatures by 0.5oC within 8 hours, more than doubling the prior stratification. Wind mixing quickly homogenized the water column, resulting in the surface often showing the deeper upwelling and advective events. Although acoustic plumes with bubbles were observed in the water column, there was no evidence of geothermal vents or geothermal influence on temperatures. Mixing by bubbles rising in the water column was indistinguishable from the wind and tidal mixing, although the strongest upward vertical velocities were observed at the sites of these acoustic/bubble plumes.

COLD-WATER CORALS AND HYDROCHEMISTRY - is there a unifying link?

NASA Astrophysics Data System (ADS)

Flögel, Sascha; Rüggeberg, Andres; Mienis, Furu; Dullo, Wolf-Christian

2010-05-01

Physical and chemical parameters were measured in five different regions of the Northeast Atlantic with known occurrences of cold-water coral reefs and mounds and in the Mediterranean, where these corals form living carpets over existing morphologies. In this study we analyzed 282 bottom water samples regarding delta13CDIC, delta18O, and DIC. The hydrochemical data reveal characteristic patterns and differences for cold-water coral sites with living coral communities and ongoing reef and mound growth at the Irish and Norwegian sites. While the localities in the Mediterranean, in the Gulf of Cadiz, and off Mauritania show only patchy coral growth on mound-like reliefs and various substrates. The analysis of delta13C/delta18O reveals distinct clusters for the different regions and the respective bottom water masses bathing the delta18O, and especially between delta13CDIC and DIC shows that DIC is a parameter with high sensitivity to the mixing of bottom water masses. It varies distinctively between sites with living reefs/mounds and sites with restricted patchy growth or dead corals. Results suggest that DIC and delta13CDIC can provide additional insights into the mixing of bottom water masses. Prolific cold-water coral growth forming giant biogenic structures plot into a narrow geochemical window characterized by a variation of delta13CDIC between 0.45 and 0.79 per mille being associated with the water mass having a density of sigma-theta of 27.5±0.15 kg m-3.

Guidance for Subaqueous Dredged Material Capping.

DTIC Science & Technology

1998-06-01

from Ambrose Channel , over the contaminated sediments. At least two intermediate sur- veys and additional capping were required before capping was...organisms to a given bioturbation depth; reducing contami- nant flux rates to achieve specific sediment, pore water, or water column target...bathymetry, bottom slopes, cur- rents, water depths, water column density stratification, erosion/accretion trends, proximity to navigation channels

Note On The Ross Sea Shelf Water Downflow Processes (antarctica)

NASA Astrophysics Data System (ADS)

Bergamasco, A.; Defendi, V.; Spezie, G.; Budillon, G.; Carniel, S.

In the framework of the CLIMA Project of the Italian National Program for Research in Antarctica, three different experimental data sets were acquired along the continental shelf break; two of them (in 1997 and 2001) close to Cape Adare, the 1998 one in the middle of the Ross Sea (i.e. 75 S, 177 W). The investigations were chosen in order to explore the downslope flow of the bottom waters produced in the Ross Sea, namely the High Salinity Shelf Water (HSSW, the densest water mass of the southern ocean coming from its formation site in the polynya region in Terra Nova bay), and the Ice Shelf Water (ISW, originated below the Ross Ice Shelf and outflowing northward). Both bottom waters spill over the shelf edge and mix with the Circumpolar Deep Water (CDW) contributing to the formation of the Antarctic Bottom Waters (AABW). Interpreting temperature, salinity and density maps in terms of cascading processes, both HSSW and ISW overflows are evidenced during, respectively, 1997 and 1998. During the 2001 acquisition there is no presence of HSSW along the shelf break, nevertheless distribution captures the evidence of a downslope flow process.

A Synoptic View of the Ventilation and Circulation of Antarctic Bottom Water from Chlorofluorocarbons and Natural Tracers

NASA Astrophysics Data System (ADS)

Purkey, Sarah G.; Smethie, William M.; Gebbie, Geoffrey; Gordon, Arnold L.; Sonnerup, Rolf E.; Warner, Mark J.; Bullister, John L.

2018-01-01

Antarctic Bottom Water (AABW) is the coldest, densest, most prolific water mass in the global ocean. AABW forms at several distinct regions along the Antarctic coast and feeds into the bottom limb of the meridional overturning circulation, filling most of the global deep ocean. AABW has warmed, freshened, and declined in volume around the globe in recent decades, which has implications for the global heat and sea level rise budgets. Over the past three decades, the use of tracers, especially time-varying tracers such as chlorofluorocarbons, has been essential to our understanding of the formation, circulation, and variability of AABW. Here, we review three decades of temperature, salinity, and tracer data and analysis that have led to our current knowledge of AABW and how the southern component of deep-ocean ventilation is changing with time.

A Synoptic View of the Ventilation and Circulation of Antarctic Bottom Water from Chlorofluorocarbons and Natural Tracers.

PubMed

Purkey, Sarah G; Smethie, William M; Gebbie, Geoffrey; Gordon, Arnold L; Sonnerup, Rolf E; Warner, Mark J; Bullister, John L

2018-01-03

Antarctic Bottom Water (AABW) is the coldest, densest, most prolific water mass in the global ocean. AABW forms at several distinct regions along the Antarctic coast and feeds into the bottom limb of the meridional overturning circulation, filling most of the global deep ocean. AABW has warmed, freshened, and declined in volume around the globe in recent decades, which has implications for the global heat and sea level rise budgets. Over the past three decades, the use of tracers, especially time-varying tracers such as chlorofluorocarbons, has been essential to our understanding of the formation, circulation, and variability of AABW. Here, we review three decades of temperature, salinity, and tracer data and analysis that have led to our current knowledge of AABW and how the southern component of deep-ocean ventilation is changing with time.

Bottom Topographic Changes of Poyang Lake During Past Decade Using Multi-temporal Satellite Images

NASA Astrophysics Data System (ADS)

Zhang, S.

2015-12-01

Poyang Lake, as a well-known international wetland in the Ramsar Convention List, is the largest freshwater lake in China. It plays crucial ecological role in flood storage and biological diversity. Poyang Lake is facing increasingly serious water crises, including seasonal dry-up, decreased wetland area, and water resource shortage, all of which are closely related to progressive bottom topographic changes over recent years. Time-series of bottom topography would contribute to our understanding of the lake's evolution during the past several decades. However, commonly used methods for mapping bottom topography fail to frequently update quality bathymetric data for Poyang Lake restricted by weather and accessibility. These deficiencies have limited our ability to characterize the bottom topographic changes and understanding lake erosion or deposition trend. To fill the gap, we construct a decadal bottom topography of Poyang Lake with a total of 146 time series medium resolution satellite images based on the Waterline Method. It was found that Poyang Lake has eroded with a rate of -14.4 cm/ yr from 2000 to 2010. The erosion trend was attributed to the impacts of human activities, especially the operation of the Three Gorge Dams, sand excavation, and the implementation of water conservancy project. A decadal quantitative understanding bottom topography of Poyang Lake might provide a foundation to model the lake evolutionary processes and assist both researchers and local policymakers in ecological management, wetland protection and lake navigation safety.

Resurvey of quality of surface water and bottom material of the Barataria Preserve of Jean Lafitte National Historical Park and Preserve, Louisiana, 1999-2000

USGS Publications Warehouse

Swarzenski, Christopher M.

2003-01-01

The quality of water and bottom material in the Barataria Preserve of Jean Lafitte National Historical Park and Preserve, Louisiana, was surveyed from March 1999 to May 2000. Organochlorine, chlorophenoxy acid, and organophosphorus pesticides; polychlorinated biphenyls (PCB?s); and trace elements were analyzed in surface water and bottom material from three sites previously sampled in a 1981-82 survey. Surface water at six sites was sampled and analyzed for selected nutrients and major inorganic ions based on their importance to human health, the health of the marshes of the Barataria Preserve, or their usefulness in tracking the circulation of Mississippi River water in the Barataria Preserve. Southern Louisiana was in a moderate to severe drought during most of the sampling period, which elevated salinity in the Barataria Preserve for at least 8 months. Specific conductance values were less than 3,000 ?S/cm (microsiemens per centimeter at 25 degrees Celsius) in surface water throughout the Barataria Preserve from March through September 1999. Specific conductance values increased over the next 2 months and then remained between 5,000 and 6,000 ?S/cm. The herbicide 2,4-D was detected in water at the two sites sampled in August 1999 but not at any site during the two other sampling times. Iron, manganese, and the trace elements copper, nickel, and zinc were detected in dissolved and whole-water samples at all three sites. Nitrite+ nitrate, as nitrogen, concentrations ranged from less than 0.002 to 0.19 mg/L (milligrams per liter). Ammonia, as nitrogen, concentrations ranged from less than 0.01 to 0.16 mg/L. Orthophosphate, as phosphorus, concentrations ranged from less than 0.002 to 0.14 mg/L. Calcium, magnesium, potassium, sulfate, and chloride concentrations in surface water were elevated due to the marine influence on the composition of surface water in the Barataria Preserve during the sampling period. Sulfate and chloride concentrations reached 379 and 2,830 mg/L, respectively. Polychlorinated biphenyls, chlordane, and DDT were detected in bottom material. Trace elements were detected in bottom material at all three of the sampled sites. Arsenic concentrations ranged from 4 to 9 ?g/g (micrograms per gram) and lead concentrations from 20 to 31 ?g/g. Mercury concentrations also were above laboratory reporting levels (LRL?s) for bottom material at all three sites. The herbicide 2,4-D was detected in surface water during both surveys. Other organic compounds were not detected in surface water. Mercury and chromium were detected in surface water at all three sites during the 1981-82 survey but were below LRL?s during the 1999-2000 survey. Changes in chemical characteristics of bottom material occurred during the years between the 1981-82 and 1999-2000 surveys. DDT decreased in the bottom material at Bayou Segnette near Barataria. DDE, a degradation product, increased at this site, indicating that over time, DDT concentrations are decreasing in bottom material. PCB?s were present in similar concentrations (Bayou Segnette near Barataria) or increased (Bayou Segnette 4.6 miles below Westwego) from 1981-82 to 1999-2000. Cadmium concentrations consistently decreased by half or more at all three sites from 1981-82 to 1999-2000. Mercury concentrations were consistently lower at all three sites in the 1999-2000 survey, but the differences from the 1981-82 survey were small. Chromium concentrations increased at two of the three sites from 1981-82 to the present survey. At the third site, no chromium value was available for the earlier survey. Concentrations of copper and nickel increased in bottom material at the two sites on Bayou Segnette, but decreased at Kenta Canal northwest of Westwego. Probable Effects Levels (PEL?s) and Interim Sediment Quality Guidelines (ISQG?s) concentrations, as tabulated by the Canadian Council of Ministers of the

Bottom-boundary-layer measurements on the continental shelf off the Ebro River, Spain

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.; Losada, M.A.; Medina, R.

1990-01-01

Measurements of currents, waves and light transmission obtained with an instrumented bottom tripod (GEOPROBE) were used in conjunction with a theoretical bottom-boundary-layer model for waves and currents to investigate sediment transport on the continental shelf south of the Ebro River Delta, Spain. The current data show that over a 48-day period during the fall of 1984, the average transport at 1 m above the seabed was alongshelf and slightly offshore toward the south-southwest at about 2 cm/s. A weak storm passed through the region during this period and caused elevated wave and current speeds near the bed. The bottom-boundary-layer model predicted correspondingly higher combined wave and current bottom shear velocities at this time, but the GEOPROBE optical data indicate that little to no resuspension occurred. This result suggests that the fine-grained bottom sediment, which has a clay component of 80%, behaves cohesively and is more difficult to resuspend than noncohesive materials of similar size. Model computations also indicate that noncohesive very fine sand in shallow water (20 m deep) was resuspended and transported mainly as bedload during this storm. Fine-grained materials in shallow water that are resuspended and transported as suspended load into deeper water probably account for the slight increase in sediment concentration at the GEOPROBE sensors during the waning stages of the storm. The bottom-boundary-layer data suggest that the belt of fine-grained bottom sediment that extends along the shelf toward the southwest is deposited during prolonged periods of low energy and southwestward bottom flow. This pattern is augmented by enhanced resuspension and transport toward the southwest during storms. ?? 1990.

Electromagnetic Surveying in the Mangrove Lakes Region of Everglades National Park

NASA Astrophysics Data System (ADS)

Whitman, D.; Price, R.; Frankovich, T.; Fourqurean, J.

2015-12-01

The Mangrove Lakes are an interconnected set of shallow (~ 1m), brackish lake and creek systems on the southern margin of the Everglades adjacent to Florida Bay. Current efforts associated with the Comprehensive Everglades Restoration Plan (CERP) aim to increase freshwater flow into this region. This study describes preliminary results of geophysical surveys in the lakes conducted to assess changes in the groundwater chemistry as part of a larger hydrologic and geochemical study in the Everglades Lakes region. Marine geophysical profiles were conducted in Alligator Creek (West Lake) and McCormick Creek systems in May, 2014. Data included marine electromagnetic (EM) profiles and soundings, water depth measurements, surface water conductivity and salinity measurements. A GSSI Profiler EMP-400 multi-frequency EM conductivity meter continuously recorded in-phase and quadrature field components at 1, 8, and 15 KHz. The system was deployed in a flat bottomed plastic kayak towed behind a motorized skiff. Lake water depths were continuously measured with a sounder/chart plotter which was calibrated with periodic sounding rod measurements. At periodic intervals during the survey, the profiling was stopped and surface water conductivity, temperature and salinity are recorded with a portable YSI probe on the tow boat. Over 40,000 discrete 3-frequency EM measurements were collected. The data were inverted to 2-layer models representing the water layer thickness and conductivity and the lake bottom conductivity. At spot locations, models were constrained with water depth soundings and surface water conductivity measurements. At other locations along the profiles, the water depth and conductivity were allowed to be free, but the free models were generally consistent with the constrained models. Multilayer sub-bottom models were also explored but were found to be poorly constrained. In West Lake, sub-bottom conductivities decreased from 400 mS/m in the west to 200 mS/m in the east indicating a general W to E decrease in groundwater salinity. In the McCormick Creek system, sub-bottom conductivities increased from 200 mS/m at the north end of Seven Palm Lake to over 650 mS/m at the southern end of Monroe Lake indicating a general N to S increase in ground water salinity. Additional profiles are planned in August, 2015.

Abyssal Upwelling in Mid-Ocean Ridge Fracture Zones

NASA Astrophysics Data System (ADS)

Clément, Louis; Thurnherr, Andreas M.

2018-03-01

Turbulence in the abyssal ocean plays a fundamental role in the climate system by sustaining the deepest branch of the overturning circulation. Over the western flank of the Mid-Atlantic Ridge in the South Atlantic, previously observed bottom-intensified and tidally modulated mixing of abyssal waters appears to imply a counterintuitive densification of deep and bottom waters. Here we show that inside fracture zones, however, turbulence is elevated away from the seafloor because of intensified downward propagating near-inertial wave energy, which decays below a subinertial shear maximum. Ray-tracing simulations predict a decay of wave energy subsequent to wave-mean flow interactions. The hypothesized wave-mean flow interactions drive a deep flow toward lighter densities of up to 0.6 Sv over the mid-ocean ridge flank in the Brazil Basin, and the same process may also cause upwelling of abyssal waters in other ocean basins with mid-ocean ridges with fracture zones.

Climate-induced warming of lakes can be either amplified or suppressed by trends in water clarity

USGS Publications Warehouse

Rose, Kevin C.; Winslow, Luke A.; Read, Jordan S.; Hansen, Gretchen J. A.

2016-01-01

Climate change is rapidly warming aquatic ecosystems including lakes and reservoirs. However, variability in lake characteristics can modulate how lakes respond to climate. Water clarity is especially important both because it influences the depth range over which heat is absorbed, and because it is changing in many lakes. Here, we show that simulated long-term water clarity trends influence how both surface and bottom water temperatures of lakes and reservoirs respond to climate change. Clarity changes can either amplify or suppress climate-induced warming, depending on lake depth and the direction of clarity change. Using a process-based model to simulate 1894 north temperate lakes from 1979 to 2012, we show that a scenario of decreasing clarity at a conservative yet widely observed rate of 0.92% yr−1 warmed surface waters and cooled bottom waters at rates comparable in magnitude to climate-induced warming. For lakes deeper than 6.5 m, decreasing clarity was sufficient to fully offset the effects of climate-induced warming on median whole-lake mean temperatures. Conversely, a scenario increasing clarity at the same rate cooled surface waters and warmed bottom waters relative to baseline warming rates. Furthermore, in 43% of lakes, increasing clarity more than doubled baseline bottom temperature warming rates. Long-term empirical observations of water temperature in lakes with and without clarity trends support these simulation results. Together, these results demonstrate that water clarity trends may be as important as rising air temperatures in determining how waterbodies respond to climate change.

Pumping bottom water to prevent Korean red tide damage caused by Cochlodinium polykrikoides Margalef.

PubMed

Cho, Eun Seob; Moon, Seong Yong; Shu, Young Sang; Hwang, Jae Dong; Youn, Seok Hyun

2015-09-01

Cochlodinium polykrikoides Margalef produces annual massive blooms in Korean coastal waters which cause great damage to aquaculture and fisheries. Although various methods have been developed to remove the red tide of C. polykrikoides, release of yellow loess has been regarded as the most desirable technique for mitigation for over 10 years. Each August, strong irradiation generates water column stratification separating warm surface from colder bottom waters. Water from a distance of 0 (St. 1), 5 (St. 2), 10 (St. 3), and 15 m (St. 4) was pumped by running a pump for 0, 10, 30 and 90 min and characterized water temperature, salinity collected, suspended solids, Chl-a, and phytoplankton including C. polykrikoides. After running for 30 min, was temperature and salinity in surface water was similar to those of bottom water, and water column stratification completely reversed after 90 min. Likewise, suspended solids, Chl-a, and total phytoplankton cell density decreased after 30 min, but C. polykrikoides did not show strong removal because of low cell density during sampling. However, the number of C. polykrikoides was significantly diluted (80%) after 90 min. These results suggested that pumping device was as an environmentally-friendly method convenient to be install in fish cages and effective to remove C. polykrikoides stratified water column conditions.

Investigating the Sources of Decadal-Scale Property Changes in Antarctic Bottom Water in the Southeast Indian Ocean (80-90°E)

NASA Astrophysics Data System (ADS)

Gottschalk, K.; Macdonald, A. M.

2016-12-01

A recognizable warming and freshening of Antarctic Bottom Water (AABW) throughout much of the Southern Ocean is one of the major findings of the international long-line hydrographic programs of 1990's and the 2000's. A recent GO-SHIP repeat of the I08S line in the southeast Indian Ocean in 2016 found continued, but weaker, AABW warming and significantly strong freshening in the Antarctic-Australian Basin (A-AB). It has been proposed that the 2010 B9b iceberg calving along the Adélie Land Coast may be linked to the sharp increase in A-AB AABW freshening. The present study seeks to affirm or challenge this hypothesis through a quantitative investigation into the origins of A-AB (i.e. I08S) bottom water. The investigation takes the form of an Extended Optimum MultiParameter mixing analysis (eOMP) to determine a) the contribution of individual formation regions to the bottom water seen at I08S, and b) how these contributions may have changed over the twenty years since the first occupation of the line. The initial investigation that used mean source water properties found Adélie Bottom Water (ADLBW) to be the dominant source of AABW in the A-AB. However, by calculating source water properties from times preceding the occupations of the I08S line (1994, 2007, 2016), it was determined that in both 1994 and 2007, Ross Sea Bottom Water (RSBW) was the dominant source of AABW (approx. 61 & 75 %, respectively) in the A-AB. This dominance shifted in 2016, to ADLBW composing approximately 44% of AABW. This result suggests that it is feasible that the B9b calving that impacted ADLBW in the formation region is, at least, partially responsible for the changes seen at I08S. Nevertheless, given that there are significant contributions from both RSBW and Weddell Sea Bottom Water, it seems unlikely that this single alteration of ADLBW is the sole driver of the observed freshening. Further investigation seeks to determine the sensitivity of the solution to particular source water definitions and to the specific property budgets used to constrain the system.

Modeling water mass formation in the Mertz Glacier Polynya and Adélie Depression, East Antarctica

NASA Astrophysics Data System (ADS)

Marsland, S. J.; Bindoff, N. L.; Williams, G. D.; Budd, W. F.

2004-11-01

High rates of sea ice growth and brine rejection in the Mertz Glacier Polynya drive the production of dense continental shelf waters in the Adélie Depression. We consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form Adélie Land Bottom Water (ALBW). Along with Weddell and Ross Sea Bottom Waters, the ALBW is an important source of Antarctic Bottom Water. The relevant processes are modeled using a variant of the Max Planck Institute Ocean Model (MPIOM) under daily NCEP-NCAR reanalysis forcing for the period 1991-2000. The orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest. The modeled Mertz Glacier Polynya is realistic in location and extent, exhibiting low ice thickness (<0.4 m) and low ice fraction (<50%). The net surface ocean to atmosphere heat flux exceeds 200 W m2 and is dominated by sensible heat exchange. In wintertime (May through September inclusive), 7.5 m of sea ice forms over the Adélie Depression at a rate of 4.9 cm d-1: this results in annual average volumetric production of 99 km3 of sea ice. The associated brine release drives dense shelf water formation. The off-shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning. Averaged over the period 1991-2000 the off shelf flow of dense water is 0.15 Sv: for a period of strong outflow (1993-1997), this increases to 0.24 Sv. Most of the outflow occurs during July through October, at a rate of 0.40 (0.63) Sv over the period 1991-2000 (1993-1997). The peak mean monthly outflow can exceed 1 Sv.

Eutrophication and Hypoxia Degrade Ecosystem Functions and Services of Narragansett Bay Benthic Communities

EPA Science Inventory

Excessive input of nitrogen to estuaries and coastal waters leads to eutrophication; the resulting organic matter over-enrichment of the sediments and seasonal hypoxia of the bottom water have well-known deleterious effects on benthic community biodiversity, abundance, and biomas...

Eutrophication and Hypoxia Diminish Ecosystem Functions of Benthic Communities in a New England Estuary

EPA Science Inventory

Excessive input of nitrogen to estuaries and coastal waters leads to eutrophication; the resulting organic matter over-enrichment of sediments and seasonal hypoxia of bottom water have significant deleterious effects on benthic community biodiversity, abundance, and biomass. Our ...

Wind effects on water and salt loss in playa lakes

NASA Astrophysics Data System (ADS)

Torgersen, T.

1984-10-01

The theory behind wind stress induced setup of water surface slope on a playa lake is reviewed. Due to the low gradient of the bottom in most playa lakes (1-20 cm km -1), the advance and retreat of lake waters due to wind stress can expose or cover many square kilometers. It is even possible for the surface slope to exceed the bottom slope and thereby create a "roving" lake. Such water movements can transport lake water over undersaturated "shore" sediments and water can therefore infiltrate and be lost without an increase in lake salinity. This case is demonstrated with data from Lake George, New South Wales, Australia. Such wind effects need to be examined for their relation to the diagenesis of sediments, the composition of the bitterns, and the salt budget of playa lakes.

A Study of Baroclinic Instability Induced Convergence Near the Bottom Using Water Age Simulations

NASA Astrophysics Data System (ADS)

Zhang, Wenxia; Hetland, Robert D.

2018-03-01

Baroclinic instability of lateral density gradients gives way to lateral buoyancy transport, which often results in convergence of buoyancy transport. Along a sloping bottom, the induced convergence can force upward extension of bottom water. Eddy transport induced convergence at the bottom and the consequent suspended layers of bottom properties are investigated using a three-dimensional idealized model. Motivated by the distinct characteristics of intrusions over the Texas-Louisiana shelf, a series of configurations are performed with the purpose of identifying parameter impacts on the intensity of eddy transport. This study uses the "horizontal slope Burger number" as the predominant parameter; the parameter is functioned with SH=SRi-1/2=δ/Ri to identify formation of baroclinic instability, where S is the slope Burger number, δ is the slope parameter, and Ri is the Richardson number, previously shown to be the parameter that predicts the intensity of baroclinic instability on the shelf. Intrusion spreads into the interior abutting a layer that is characterized by degraded vertical stratification; a thickening in the bottom boundary layer colocates with the intrusion, which usually thins at either edge of the intrusion because of a density barrier in association with concentrated isopycnals. The intensity of convergence degrades and bottom tracer fluxes reduce linearly with increased SH on logarithmic scales, and the characteristics of bottom boundary layer behavior and the reversal in alongshore current tend to vanish.

Grain size mapping in shallow rivers using spectral information: a lab spectroradiometry perspective

NASA Astrophysics Data System (ADS)

Niroumand-Jadidi, Milad; Vitti, Alfonso

2017-10-01

Every individual attribute of a riverine environment defines the overall spectral signature to be observed by an optical sensor. The spectral characteristic of riverbed is influenced not only by the type but also the roughness of substrates. Motivated by this assumption, potential of optical imagery for mapping grain size of shallow rivers (< 1 m deep) is examined in this research. The previous studies concerned with grain size mapping are all built upon the texture analysis of exposed bed material using very high resolution (i.e. cm resolution) imagery. However, the application of texturebased techniques is limited to very low altitude sensors (e.g. UAVs) to ensure the sufficient spatial resolution. Moreover, these techniques are applicable only in the presence of exposed substrates along the river channel. To address these drawbacks, this study examines the effectiveness of spectral information to make distinction among grain sizes for submerged substrates. Spectroscopic experiments are performed in controlled condition of a hydraulic lab. The spectra are collected over a water flume in a range of water depths and bottoms with several grain sizes. A spectral convolution is performed to match the spectra to WorldView-2 spectral bands. The material type of substrates is considered the same for all the experiments with only variable roughness/size of grains. The spectra observed over dry beds revealed that the brightness/reflectance increases with the grain size across all the spectral bands. Based on this finding, the above-water spectra over a river channel are simulated considering different grain sizes in the bottom. A water column correction method is then used to retrieve the bottom reflectances. Then the inferred bottom reflectances are clustered to segregate among grain sizes. The results indicate high potential of the spectral approach for clustering grain sizes (overall accuracy of 92%) which opens up some horizons for mapping this valuable attribute of rivers using remotely sensed data.

Characteristics of Air Core and Surface Velocity for Water Flow in a Vortex Sediment-Extraction Chamber Measured by Using Photo Images and PTV Technique.

NASA Astrophysics Data System (ADS)

Yao, Hou Chang; Chyan Deng, Jan; Chao, Hsu Yu; Chih Yuan, Yang

2017-04-01

A vortex sediment-extraction chamber, consisted of cylindrical chamber, inflow system, bottom orifice and overflow weir, is used to separate sediment from sediment-laden water flow. A tangential inflow is introduced into a cylindrical chamber with a bottom orifice; thus, a strong vortex flow is produced there. Under actions of gravity and centrifugal force, heavier sediment particles are forced to move towards the bottom orifice, and relatively clear water flows over through the top overflow weir. The flow field in the cylindrical chamber consists of forced vortex and free vortex. When the bottom orifice is opened during the sediment-extraction process, an air core appears and changes with different settings. In this study, the air core and water surface velocity in the cylindrical chamber were measured by using a photo image process and particle tracking velocimetry (PTV), as well as numerically simulated by using a commercial software, Flow-3D.Laboratory experiments were conducted in a vortex chamber, having height of 130 cm and diameter of 48 cm. Five kinds of bottom orifice size from 1.0 cm to 3.0 cm and four kinds of inflow water discharge from 1,300cm3/s to 1,700 cm3/s were used while the inflow pipe of 3 cm in diameter was kept the same for all experiments. The characteristics of the air core and water surface velocity, and the inflow and outflow ratios under different experimental arrangements were observed and discussed so as to provide a better design and application for a vortex sediment-extraction chamber in the future.

Upwelling rebound, ephemeral secondary pycnoclines, and the creation of a near-bottom wave guide over the Monterey Bay continental shelf

USGS Publications Warehouse

Cheriton, Olivia M.; McPhee-Shaw, Erika E.; Storlazzi, Curt D.; Rosenberger, Kurt J.; Shaw, William J.; Raanan, Ben Y.

2014-01-01

Several sequential upwelling events were observed in fall 2012, using measurements from the outer half of the continental shelf in Monterey Bay, during which the infiltration of dense water onto the shelf created a secondary, near-bottom pycnocline. This deep pycnocline existed in concert with the near-surface pycnocline and enabled the propagation of near-bottom, cold, semidiurnal internal tidal bores, as well as energetic, high-frequency, nonlinear internal waves of elevation (IWOE). The IWOE occurred within 20 m of the bottom, had amplitudes of 8–24 m, periods of 6–45 min, and depth-integrated energy fluxes up to 200 W m−1. Iribarren numbers (<0.03) indicate that these IWOE were nonbreaking in this region of the shelf. These observations further demonstrate how regional upwelling dynamics and the resulting bulk, cross-margin hydrography is a first-order control on the ability of internal waves, at tidal and higher frequencies, to propagate through continental shelf waters.

On the dense water spreading off the Ross Sea shelf (Southern Ocean)

NASA Astrophysics Data System (ADS)

Budillon, G.; Gremes Cordero, S.; Salusti, E.

2002-07-01

In this study, current meter and hydrological data obtained during the X Italian Expedition in the Ross Sea (CLIMA Project) are analyzed. Our data show a nice agreement with previous data referring to the water masses present in this area and their dynamics. Here, they are used to further analyze the mixing and deepening processes of Deep Ice Shelf Water (DISW) over the northern shelf break of the Ross Sea. In more detail, our work is focused on the elementary mechanisms that are the most efficient in removing dense water from the shelf: either classical mixing effects or density currents that interact with some topographic irregularity in order to drop to deeper levels, or also the variability of the Antarctic Circumpolar Current (ACC) which, in its meandering, can push the dense water off the shelf, thus interrupting its geostrophic flow. We also discuss in detail the (partial) evidence of dramatic interactions of the dense water with bottom particulate, of geological or biological origin, thus generating impulsive or quasi-steady density-turbidity currents. This complex interaction allows one to consider bottom particular and dense water as a unique self-interacting system. In synthesis, this is a first tentative analysis of the effect of bottom particulate on the dense water dynamics in the Ross Sea.

Basin-Wide Temperature Constraints On Gas Hydrate Stability In The Gulf Of Mexico

NASA Astrophysics Data System (ADS)

MacDonald, I. R.; Reagan, M. T.; Guinasso, N. L.; Garcia-Pineda, O. G.

2012-12-01

Gas hydrate deposits commonly occur at the seafloor-water interface on marine margins. They are especially prevalent in the Gulf of Mexico where they are associated with natural oil seeps. The stability of these deposits is potentially challenged by fluctuations in bottom water temperature, on an annual time-scale, and under the long-term influence of climate change. We mapped the locations of natural oil seeps where shallow gas hydrate deposits are known to occur across the entire Gulf of Mexico basin based on a comprehensive review of synthetic aperture radar (SAR) data (~200 images). We prepared a bottom water temperature map based on the archive of CTD casts from the Gulf (~6000 records). Comparing the distribution of gas hydrate deposits with predicted bottom water temperature, we find that a broad area of the upper slope lies above the theoretical stability horizon for structure 1 gas hydrate, while all sites where gas hydrate deposits occur are within the stability horizon for structure 2 gas hydrate. This is consistent with analytical results that structure 2 gas hydrates predominate on the upper slope (Klapp et al., 2010), where bottom water temperatures fluctuate over a 7 to 10 C range (approx. 600 m depth), while pure structure 1 hydrates are found at greater depths (approx. 3000 m). Where higher hydrocarbon gases are available, formation of structure 2 gas hydrate should significantly increase the resistance of shallow gas hydrate deposits to destabilizing effects variable or increasing bottom water temperature. Klapp, S.A., Bohrmann, G., Kuhs, W.F., Murshed, M.M., Pape, T., Klein, H., Techmer, K.S., Heeschen, K.U., and Abegg, F., 2010, Microstructures of structure I and II gas hydrates from the Gulf of Mexico: Marine and Petroleum Geology, v. 27, p. 116-125.Bottom temperature and pressure for Gulf of Mexico gas hydrate outcrops and stability horizons for sI and sII hydrate.

The Effect of Alongcoast Advection on Pacific Northwest Shelf and Slope Water Properties in Relation to Upwelling Variability

NASA Astrophysics Data System (ADS)

Stone, Hally B.; Banas, Neil S.; MacCready, Parker

2018-01-01

The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin-scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N-50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well-explained (R2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large-scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large-scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale.

The Effect of Alongcoast Advection on Pacific Northwest Shelf and Slope Water Properties in Relation to Upwelling Variability

PubMed Central

Banas, Neil S.; MacCready, Parker

2018-01-01

Abstract The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin‐scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N–50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well‐explained (R 2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large‐scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large‐scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale. PMID:29938149

40 CFR 230.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... of a bottom surface area and any overlying volume of water. In the case of wetlands on which surface water is not present, the disposal site consists of the wetland surface area. (j) [Reserved] (k) The... available and capable of being done after taking into consideration cost, existing technology, and logistics...

40 CFR 230.3 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... of a bottom surface area and any overlying volume of water. In the case of wetlands on which surface water is not present, the disposal site consists of the wetland surface area. (j) [Reserved] (k) The... available and capable of being done after taking into consideration cost, existing technology, and logistics...

40 CFR 230.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... of a bottom surface area and any overlying volume of water. In the case of wetlands on which surface water is not present, the disposal site consists of the wetland surface area. (j) [Reserved] (k) The... available and capable of being done after taking into consideration cost, existing technology, and logistics...

40 CFR 230.3 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... of a bottom surface area and any overlying volume of water. In the case of wetlands on which surface water is not present, the disposal site consists of the wetland surface area. (j) [Reserved] (k) The... available and capable of being done after taking into consideration cost, existing technology, and logistics...

Strong Effects of a Shelfbreak Jet on Microbial Enzyme Activities

NASA Astrophysics Data System (ADS)

Hoarfrost, A.; Balmonte, J. P.; Ziervogel, K.; Ghobrial, S.; Gawarkiewicz, G.; Arnosti, C.

2016-02-01

The activities of extracellular enzymes are critical in initiating microbial cycling of organic carbon, yet the dynamics of heterotrophic enzyme activities in marine environments are still poorly understood. Variations at a given site in rates of activity and the spectrum of organic substrates hydrolyzed may depend upon environmental context. We measured the extracellular enzymatic hydrolysis of 13 high- and low-molecular-weight organic substrates in surface and bottom waters along a closely spaced 4-station transect at 71 W on the North Atlantic continental shelf, in the vicinity of the shelfbreak front. This transect intersects a robust upwelling cell that typically shows high biologic productivity, and is locatable by changes in T/S profiles and chl a concentrations along sharp spatial gradients. At the time of sampling, cold pool waters over the continental shelf were relatively cold, 3.5 Deg. C, compared to 12 Deg. C over the upper continental slope. Satellite thermal imagery indicated that shelf water extended offshore and interacted with a large crest of the Gulf Stream. The surface and bottom waters associated with the upwelling jet were characterized by enzyme activities a factor of 20 more rapid than closer inshore waters, and surface water chl a concentrations that were two to three times higher than the inshore waters. The spectrum of enzyme activities also differed markedly between surface and bottom waters both within the jet and at near-shore stations. Microbial extracellular enzymatic activities were strongly influenced by differences in their environmental context along the continental slope and shelfbreak front. Constraining the factors controlling heterotrophic activity across the diverse marine environment is an important step in understanding microbial controls on carbon cycling.

Benthic flux of dissolved nickel into the water column of south San Francisco Bay

USGS Publications Warehouse

Topping, B.R.; Kuwabara, J.S.; Parcheso, Francis; Hager, S.W.; Arnsberg, A.J.; Murphy, Fred

2001-01-01

Field and laboratory studies were conducted between April, 1998 and May, 1999 to provide the first direct measurements of the benthic flux of dissolved (0.2-micron filtered) nickel between the bottom sediment and water column at three sites in the southern component of San Francisco Bay (South Bay), California. Dissolved nickel and predominant ligands (represented by dissolved organic carbon, and sulfides) were the solutes of primary interest, although a variety of ancillary measurements were also performed to provide a framework for interpretation. Results described herein integrate information needs identified by the State Water Resources Control Board and local stakeholders with fundamental research associated with the U.S. Geological Survey Toxic Substances Hydrology Program. Dissolved-Ni concentrations in the bottom water over the three sampling dates ranged from 34 to 43 nanomoles per liter. Dissolved-macronutrient concentrations in the bottom water were consistently higher (frequently by orders of magnitude) than surface-water determinations reported for similar times and locations (Regional Monitoring Program, 2001). This is consistent with measured positive benthic fluxes for the macronutrients. Benthic-flux estimates for dissolved nickel from core-incubations, when areally averaged over the South Bay, were significant (that is, of equivalent or greater order of magnitude) relative to previously reported freshwater point and non-point sources. This observation is consistent with previous determinations for other metals, and with the potential remobilization of sediment-associated metals that have been ubiquitously distributed in the South Bay. Similar to dissolved-nickel results, benthic flux of macronutrients was also consistently significant relative to surface-water inputs. These results add to a growing body of knowledge that strongly suggests a need to consider contaminant transport across the sediment-water interface when establishing future management strategies for the watershed.

Wind Induced Sediment Resuspension in a Microtidal Estuary

NASA Technical Reports Server (NTRS)

Booth, J. G.; Miller, R. L.; McKee, B. A.; Leathers, R. A.

1999-01-01

Bottom sediment resuspension frequency, duration and extent (% of bottom sediments affected) were characterized for the fifteen month period from September 1995 to January 1997 for the Barataria Basin, LA. An empirical model of sediment resuspension as a function of wind speed, direction, fetch and water depth was derived from wave theory. Water column turbidity was examined by processing remotely sensed radiance information from visible and near-IR AVHRR imagery. Based on model predictions, wind induced resuspension occurred during all seasons of this study. Seasonal characteristics for resuspension reveal that late fall, winter and early spring are the periods of most frequent and intense resuspension. Model predictions of the critical wind speed required to induce resuspension indicate that winds of 4 m/s (averaged over all wind directions resuspend approximately 50% of bottom sediments in the water bodies examined. Winds of this magnitude (4 m/s) occurred for 80% of the time during the late fall, winter and early spring and for approximately 30% of the time during the summer. More than 50% of the bottom sedimets are resuspended throughout the year, indicating the importance of resuspension as a process affecting sediment and biogeochemical fluxes in the Barataria Basin.

Enhanced particle fluxes and heterotrophic bacterial activities in Gulf of Mexico bottom waters following storm-induced sediment resuspension

NASA Astrophysics Data System (ADS)

Ziervogel, K.; Dike, C.; Asper, V.; Montoya, J.; Battles, J.; D`souza, N.; Passow, U.; Diercks, A.; Esch, M.; Joye, S.; Dewald, C.; Arnosti, C.

2016-07-01

Bottom nepheloid layers (BNLs) in the deep sea transport and remobilize considerable amounts of particulate matter, enhancing microbial cycling of organic matter in cold, deep water environments. We measured bacterial abundance, bacterial protein production, and activities of hydrolytic enzymes within and above a BNL that formed in the deep Mississippi Canyon, northern Gulf of Mexico, shortly after Hurricane Isaac had passed over the study area in late August 2012. The BNL was detected via beam attenuation in CTD casts over an area of at least 3.5 km2, extending up to 200 m above the seafloor at a water depth of 1500 m. A large fraction of the suspended matter in the BNL consisted of resuspended sediments, as indicated by high levels of lithogenic material collected in near-bottom sediment traps shortly before the start of our sampling campaign. Observations of suspended particle abundance and sizes throughout the water column, using a combined camera-CTD system (marine snow camera, MSC), revealed the presence of macroaggregates (>1 mm in diameter) within the BNL, indicating resuspension of canyon sediments. A distinct bacterial response to enhanced particle concentrations within the BNL was evident from the observation that the highest enzymatic activities (peptidase, β-glucosidase) and protein production (3H-leucine incorporation) were found within the most particle rich sections of the BNL. To investigate the effects of enhanced particle concentrations on bacterial activities in deep BNLs more directly, we conducted laboratory experiments with roller bottles filled with bottom water and amended with experimentally resuspended sediments from the study area. Macroaggregates formed within 1 day from resuspended sediments; by day 4 of the incubation bacterial cell numbers in treatments with resuspended sediments were more than twice as high as in those lacking sediment suspensions. Cell-specific enzymatic activities were also generally higher in the sediment-amended compared to the unamended treatments. The broader range and higher activities of polysaccharide hydrolases in the presence of resuspended sediments compared to the unamended water reflected enzymatic capabilities typical for benthic bacteria. Our data suggest that the formation of BNLs in the deep Gulf of Mexico can lead to transport of sedimentary organic matter into bottom waters, stimulating bacterial food web interactions. Such storm-induced resuspension may represent a possible mechanism for the redistribution of sedimented oil-fallout from the Deepwater Horizon spill in 2010.

Marine bacterioplankton community turnover within seasonally hypoxic waters of a subtropical sound: Devil's Hole, Bermuda.

PubMed

Parsons, Rachel J; Nelson, Craig E; Carlson, Craig A; Denman, Carmen C; Andersson, Andreas J; Kledzik, Andrew L; Vergin, Kevin L; McNally, Sean P; Treusch, Alexander H; Giovannoni, Stephen J

2015-10-01

Understanding bacterioplankton community dynamics in coastal hypoxic environments is relevant to global biogeochemistry because coastal hypoxia is increasing worldwide. The temporal dynamics of bacterioplankton communities were analysed throughout the illuminated water column of Devil's Hole, Bermuda during the 6-week annual transition from a strongly stratified water column with suboxic and high-pCO2 bottom waters to a fully mixed and ventilated state during 2008. A suite of culture-independent methods provided a quantitative spatiotemporal characterization of bacterioplankton community changes, including both direct counts and rRNA gene sequencing. During stratification, the surface waters were dominated by the SAR11 clade of Alphaproteobacteria and the cyanobacterium Synechococcus. In the suboxic bottom waters, cells from the order Chlorobiales prevailed, with gene sequences indicating members of the genera Chlorobium and Prosthecochloris--anoxygenic photoautotrophs that utilize sulfide as a source of electrons for photosynthesis. Transitional zones of hypoxia also exhibited elevated levels of methane- and sulfur-oxidizing bacteria relative to the overlying waters. The abundance of both Thaumarcheota and Euryarcheota were elevated in the suboxic bottom waters (> 10(9) cells l(-1)). Following convective mixing, the entire water column returned to a community typical of oxygenated waters, with Euryarcheota only averaging 5% of cells, and Chlorobiales and Thaumarcheota absent. © 2014 Society for Applied Microbiology and John Wiley & Sons Ltd.

Laboratory study of spectral waves over a muddy bottom

NASA Astrophysics Data System (ADS)

Maxeiner, E.; Dalrymple, R. A.

2010-12-01

The attenuation of water waves propagating over a muddy ocean floor has been studied extensively both analytically and experimentally over the past 30 years. Possible mechanisms for this include surface wave interactions with the bottom, surface wave interactions with waves formed at the water/mud interface (lutocline) and shear instability at the water/mud interface. Typically these studies have focused on monochromatic waves. Observations of wave attenuation in the field, however, are subject to a spectrum of wave frequencies and sizes. A few field studies (Sheremet and Stone, 2003; Elgar and Raubenheimer, 2008) have explored the possible effects that a wide spectrum of wave frequencies may have on wave damping mechanisms. In this study, the wave attenuation exhibited by a sea spectrum over a muddy bottom is studied experimentally in a laboratory for the first time. Using an 18 m-long wave tank at the Coastal Engineering Laboratory at Johns Hopkins University, a piston-style wave maker is used to create both monochromatic and spectral waves. A 10 m-long section of the tank floor incorporates a recessed layer of kaolinite clay which subsequently mixes with the overlying water in the presence of waves. Testing consists of three phases. First, a series of monochromatic wave trains are produced over a range of wave frequencies and in a range of water depths to assess the damping behavior with respect to a variety of parameters such as wave frequency, wave height and water depth. Damping is assessed by comparing wave height at various longitudinal locations in the tank. Second, “wave beats” are created by superimposing waves of two frequencies to create a longer envelope. Third, the wave maker is used to generate a representative random sea condition, based on the Pierson-Moskowitz sea spectrum. For this type of testing, damping is assessed by measuring wave energy flux over a period of time at various longitudinal locations in the tank. Spectral analysis is also performed at these locations to track changing spectral energy, as previous studies have hypothesized mechanisms of energy transfer between waves of different frequencies. This study is part of a Multidisciplinary University Research Initiative (MURI), which includes on computational, laboratory and field studies of wave damping in nearshore areas of the Gulf of Mexico along the coast of Louisiana.

Occurrence and distribution of bacterial indicators and pathogens in canal communities along the Texas coast.

PubMed

Goyal, S M; Gerba, C P; Melnick, J L

1977-08-01

Increased construction of residential canal communities along the southern coastline of the United States has led to a concern about their impact on water quality. Pollution of such dead-end canals is potentially hazardous because of their heavy usage for recreational activities. Coliforms, fecal coliforms, and salmonellae in the surface water and bottom sediments of six selected residential coastal canals were monitored over a period of 17 months. No statistically significant relationship was observed between the organism concentrations and temperature, pH, turbidity, and suspended solids content of water. An inverse relationship between the concentration of indicator organism and salinity of water was found, however, to occur at a 99.9% level of significance. All of the microorganisms studied were found to be present in greater numbers in sediments than in the overlying water, often by a factor of several logs. Heavy rainfall resulted in large increases in the number of organisms in both water and sediment samples. Our results indicate that bottom sediments in the shallow canal systems can act as reservoirs of enteric bacteria, which may be resuspended in response to various environmental factors and recreational activities.

Bottom friction models for shallow water equations: Manning’s roughness coefficient and small-scale bottom heterogeneity

NASA Astrophysics Data System (ADS)

Dyakonova, Tatyana; Khoperskov, Alexander

2018-03-01

The correct description of the surface water dynamics in the model of shallow water requires accounting for friction. To simulate a channel flow in the Chezy model the constant Manning roughness coefficient is frequently used. The Manning coefficient nM is an integral parameter which accounts for a large number of physical factors determining the flow braking. We used computational simulations in a shallow water model to determine the relationship between the Manning coefficient and the parameters of small-scale perturbations of a bottom in a long channel. Comparing the transverse water velocity profiles in the channel obtained in the models with a perturbed bottom without bottom friction and with bottom friction on a smooth bottom, we constructed the dependence of nM on the amplitude and spatial scale of perturbation of the bottom relief.

Nuclear reactor with low-level core coolant intake

DOEpatents

Challberg, Roy C.; Townsend, Harold E.

1993-01-01

A natural-circulation boiling-water reactor has skirts extending downward from control rod guide tubes to about 10 centimeters from the reactor vessel bottom. The skirts define annular channels about control rod drive housings that extend through the reactor vessel bottom. Recirculating water is forced in through the low-level entrances to these channels, sweeping bottom water into the channels in the process. The sweeping action prevents cooler water from accumulating at the bottom. This in turn minimizes thermal shock to bottom-dwelling components as would occur when accumulated cool water is swept away and suddenly replaced by warmer water.

Currents and water characteristics around the West Flower Garden Bank. [West Flower Garden Bank, coral reef, Texas continental shelf

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horne, D.J.

1986-01-01

The West Flower Garden Bank is a coral reef on the Texas Continental shelf. The corals on the bank are vulnerable to sediment contamination and to excess turbidity in the overlying water column. Concern for the environmental impact on this and other banks in the region exposed to nearby hydrocarbon production prompted the Bureau of Land Management to fund a data collection effort on the Texas/Louisiana shelf which provided the data analyzed here. Data analyzed includes profiles of velocity, temperature and salinity taken around the Bank in Oct., 1980 and March, 1981. Fixed current meter moorings and a dye experimentmore » conducted in the bottom boundary layer provided additional input. The data reveals a very complicated flow regime around the bank, with some intensification of flow around and over the bank but no movement of water from the bottom of the surrounding shelf up onto the bank.« less

Controls on the global distribution of contourite drifts: Insights from an eddy-resolving ocean model

NASA Astrophysics Data System (ADS)

Thran, Amanda C.; Dutkiewicz, Adriana; Spence, Paul; Müller, R. Dietmar

2018-05-01

Contourite drifts are anomalously high sediment accumulations that form due to reworking by bottom currents. Due to the lack of a comprehensive contourite database, the link between vigorous bottom water activity and drift occurrence has yet to be demonstrated on a global scale. Using an eddy-resolving ocean model and a new georeferenced database of 267 contourites, we show that the global distribution of modern contourite drifts strongly depends on the configuration of the world's most powerful bottom currents, many of which are associated with global meridional overturning circulation. Bathymetric obstacles frequently modify flow direction and intensity, imposing additional finer-scale control on drift occurrence. Mean bottom current speed over contourite-covered areas is only slightly higher (2.2 cm/s) than the rest of the global ocean (1.1 cm/s), falling below proposed thresholds deemed necessary to re-suspend and redistribute sediments (10-15 cm/s). However, currents fluctuate more frequently and intensely over areas with drifts, highlighting the role of intermittent, high-energy bottom current events in sediment erosion, transport, and subsequent drift accumulation. We identify eddies as a major driver of these bottom current fluctuations, and we find that simulated bottom eddy kinetic energy is over three times higher in contourite-covered areas in comparison to the rest of the ocean. Our work supports previous hypotheses which suggest that contourite deposition predominantly occurs due to repeated acute events as opposed to continuous reworking under average-intensity background flow conditions. This suggests that the contourite record should be interpreted in terms of a bottom current's susceptibility to experiencing periodic, high-speed current events. Our results also highlight the potential role of upper ocean dynamics in contourite sedimentation through its direct influence on deep eddy circulation.

Distribution and transport of suspended particulate matter in Monterey Canyon, California

USGS Publications Warehouse

Xu, J. P.; Noble, M.; Eittreim, S.L.; Rosenfeld, L.K.; Schwing, F.B.; Pilskaln, C.H.

2002-01-01

From August 1993 to August 1994, six moorings that measure current, temperature, salinity, and water clarity were deployed along the axis of Monterey Canyon to study the circulation and transport of water and suspended particulate matter through the canyon system. The moorings occupied three sites that are morphologically different: a narrow transverse section (axis width 900 m) at 1450 m water depth, a wide transverse section at 2837 m, and a third site in the fan valley axis farther offshore at 3223 m that recorded for 3 yr. In addition, CTD/transmissometer casts were conducted within and near the Monterey Canyon during four cruises. Our data show a mainly biogenic, surface turbid layer, a limited intermediate nepheloid layer, and a bottom nepheloid layer. There is a consistent presence of a turbid layer within the canyon at a water depth of about 1500 m. Tidal flow dominates at all sites, but currents above the canyon rim and within the canyon appear to belong to two distinct dynamic systems. Bottom intensification of currents plays an important role in raising the near-bottom shear stress high enough that bottom sediments are often, if not always, resuspended. Mean flow pattern suggests a convergence zone between the narrow and wide site: the near-bed (100 m above bottom where the lowest current meter was located) mean transport is down-canyon at the 1450-m site, while the near-bottom transport at the 2837-m site is up-canyon, at a smaller magnitude. Transport at the 3223-m site is dominantly NNW, cross-canyon, with periods of up-canyon flow over 3 yr. A very high-turbidity event was recorded 100 m above the canyon bottom at the narrow site. The event started very abruptly and lasted more than a week. This event was not detected at either of the deeper sites. A canyon head flushing event is likely the cause. ?? 2002 Elsevier Science B.V. All rights reserved.

Tracing groundwater input into Lake Vanda, Wright Valley, Antarctica using major ions, stable isotopes and noble gas

NASA Astrophysics Data System (ADS)

Dowling, C. B.; Poreda, R. J.; Snyder, G. T.

2008-12-01

The McMurdo Dry Valleys (MDV), Antarctica, is the largest ice-free region on Antarctica. Lake Vanda, located in central Wright Valley, is the deepest lake among the MDV lakes. It has a relatively fresh water layer above 50 m with a hypersaline calcium-chloride brine below (50-72 m). The Onyx River is the only stream input into Lake Vanda. It flows westward from the coastal Lower Wright Glacier and discharges into Lake Vanda. Suggested by the published literature and this study, there has been and may still be groundwater input into Lake Vanda. Stable isotopes, major ions, and noble gas data from this study coupled with previously published data indicate that the bottom waters of Lake Vanda have had significant contributions from a deep groundwater system. The dissolved gas of the bottom waters of Lake Vanda display solubility concentrations rather than the Ar-enriched dissolved gas seen in the Taylor Valley lakes (such as Lake Bonney). The isotopic data indicate that the bottom calcium-chloride-brine of Lake Vanda has undergone very little evaporation. The calcium-chloride chemistry of the groundwater that discharges into Lake Vanda most likely results from the chemical weathering and dissolution of cryogenic evaporites (antarcticite and gypsum) within the glacial sediments of Wright Valley. The high calcium concentrations of the brine have caused gypsum to precipitate on the lake bottom. Our work also supports previous physical and chemical observations suggesting that the upper portion actively circulates and the hypersaline bottom layer does not. The helium and calcium chloride values are concentrated at the bottom, with a very narrow transition layer between it and the above fresh water. If the freshwater layer did not actively circulate, then diffusion over time would have caused the helium and calcium chloride to slowly permeate upwards through the water column.

Chemical evolution of the Salton Sea, California: Nutrient and selenium dynamics

USGS Publications Warehouse

Schroeder, R.A.; Orem, W.H.; Kharaka, Y.K.

2002-01-01

The Salton Sea is a 1000-km2 terminal lake located in the desert area of southeastern California. This saline (???44 000 mg l-1 dissolved solids) lake started as fresh water in 1905-07 by accidental flooding of the Colorado River, and it is maintained by agricultural runoff of irrigation water diverted from the Colorado River. The Salton Sea and surrounding wetlands have recently acquired substantial ecological importance because of the death of large numbers of birds and fish, and the establishment of a program to restore the health of the Sea. In this report, we present new data on the salinity and concentration of selected chemicals in the Salton Sea water, porewater and sediments, emphasizing the constituents of concern: nutrients (N and P), Se and salinity. Chemical profiles from a Salton Sea core estimated to have a sedimentation rate of 2.3 mm yr-1 show increasing concentrations of OC, N, and P in younger sediment that are believed to reflect increasing eutrophication of the lake. Porewater profiles from two locations in the Sea show that diffusion from bottom sediment is only a minor source of nutrients to the overlying water as compared to irrigation water inputs. Although loss of N and Se by microbial-mediated volatilization is possible, comparison of selected element concentrations in river inputs and water and sediments from the Salton Sea indicates that most of the N (from fertilizer) and virtually all of the Se (delivered in irrigation water from the Colorado River) discharged to the Sea still reside within its bottom sediment. Laboratory simulation on mixtures of sediment and water from the Salton Sea suggest that sediment is a potential source of N and Se to the water column under aerobic conditions. Hence, it is important that any engineered changes made to the Salton Sea for remediation or for transfer of water out of the basin do not result in remobilization of nutrients and Se from the bottom sediment into the overlying water.

Evidence of deep circulation in two perennially ice-covered Antarctic lakes

USGS Publications Warehouse

Tyler, S.W.; Cook, P.G.; Butt, A.Z.; Thomas, J.M.; Doran, P.T.; Lyons, W.B.

1998-01-01

The perennial ice covers found on many of the lakes in the McMurdo Dry Valley region of the Antarctic have been postulated to severely limit mixing and convective turnover of these unique lakes. In this work, we utilize chlorofluorocarbon (CFC) concentration profiles from Lakes Hoare and Fryxell in the McMurdo Dry Valley to determine the extent of deep vertical mixing occurring over the last 50 years. Near the ice-water interface, CFC concentrations in both lakes were well above saturation, in accordance with atmospheric gas supersaturations resulting from freezing under the perennial ice covers. Evidence of mixing throughout the water column at Lake Hoare was confirmed by the presence of CFCs throughout the water column and suggests vertical mixing times of 20-30 years. In Lake Fryxell, CFC-11, CFC-12, and CFC-113 were found in the upper water column; however, degradation of CFC-11 and CFC-12 in the anoxic bottom waters appears to be occurring with CFC-113 only present in these bottom waters. The presence of CFC-113 in the bottom waters, in conjunction with previous work detecting tritium in these waters, strongly argues for the presence of convective mixing in Lake Fryxell. The evidence for deep mixing in these lakes may be an important, yet overlooked, phenomenon in the limnology of perennially ice-covered lakes.

Locating hot and cold-legs in a nuclear powered steam generation system

DOEpatents

Ekeroth, D.E.; Corletti, M.M.

1993-11-16

A nuclear reactor steam generator includes a reactor vessel for heating water and a steam generator with a pump casing at the lowest point on the steam generator. A cold-leg pipe extends horizontally between the steam generator and the reactor vessel to return water from the steam generator to the reactor vessel. The bottom of the cold-leg pipe is at a first height above the bottom of the reactor vessel. A hot-leg pipe with one end connected to the steam generator and a second end connected to the reactor vessel has a first pipe region extending downwardly from the steam generator to a location between the steam generator and the reactor vessel at which a bottom of the hot-leg pipe is at a second height above the bottom of the reactor vessel. A second region extends from that location in a horizontal direction at the second height to the point at which the hot-leg pipe connects to the reactor vessel. A pump is attached to the casing at a location below the first and second heights and returns water from the steam generator to the reactor vessel over the cold-leg. The first height is greater than the second height and the bottom of the steam generator is at a height above the bottom of the reactor vessel that is greater than the first and second heights. A residual heat recovery pump is below the hot-leg and has an inlet line from the hot-leg that slopes down continuously to the pump inlet. 2 figures.

Locating hot and cold-legs in a nuclear powered steam generation system

DOEpatents

Ekeroth, Douglas E.; Corletti, Michael M.

1993-01-01

A nuclear reactor steam generator includes a reactor vessel for heating water and a steam generator with a pump casing at the lowest point on the steam generator. A cold-leg pipe extends horizontally between the steam generator and the reactor vessel to return water from the steam generator to the reactor vessel. The bottom of the cold-leg pipe is at a first height above the bottom of the reactor vessel. A hot-leg pipe with one end connected to the steam generator and a second end connected to the reactor vessel has a first pipe region extending downwardly from the steam generator to a location between the steam generator and the reactor vessel at which a bottom of the hot-leg pipe is at a second height above the bottom of the reactor vessel. A second region extends from that location in a horizontal direction at the second height to the point at which the hot-leg pipe connects to the reactor vessel. A pump is attached to the casing at a location below the first and second heights and returns water from the steam generator to the reactor vessel over the cold-leg. The first height is greater than the second height and the bottom of the steam generator is at a height above the bottom of the reactor vessel that is greater than the first and second heights. A residual heat recovery pump is below the hot-leg and has an inlet line from the hot-leg that slopes down continuously to the pump inlet.

Dissolved oxygen saturation controls PAH biodegradation in freshwater estuary sediments.

PubMed

Boyd, T J; Montgomery, M T; Steele, J K; Pohlman, J W; Reatherford, S R; Spargo, B J; Smith, D C

2005-02-01

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants in terrestrial and aquatic environments and can represent a significant constituent of the carbon pool in coastal sediments. We report here the results of an 18-month seasonal study of PAH biodegradation and heterotrophic bacterial production and their controlling biogeochemical factors from 186 sediment samples taken in a tidally influenced freshwater estuary. For each sampling event, measurements were averaged from 25-45 stations covering approximately 250 km(2). There was a clear relationship between bacterial production and ambient temperature, but none between production and bottom water dissolved oxygen (DO) % saturation or PAH concentrations. In contrast with other studies, we found no effect of temperature on the biodegradation of naphthalene, phenanthrene, or fluoranthene. PAH mineralization correlated with bottom water DO saturation above 70% (r(2) > 0.99). These results suggest that the proportional utilization of PAH carbon to natural organic carbon is as much as three orders of magnitude higher during cooler months, when water temperatures are lower and DO % saturation is higher. Infusion of cooler, well-oxygenated water to the water column overlying contaminated sediments during the summer months may stimulate PAH metabolism preferentially over non-PAH organic matter.

Latest Paleocene benthic extinction event on the southern Tethyan shelf (Egypt): Foraminiferal stable isotopic (δ13C, δ18O) records

NASA Astrophysics Data System (ADS)

Schmitz, B.; Speijer, R. P.; Aubry, M.-P.

1996-04-01

The dramatic global extinction of 35% 50% of benthic foraminifera species in the deep sea in the latest Paleocene and associated negative excursions in δ13C and δ18O may be related to spreading of warm, saline bottom water from subtropical Tethyan shallow regions over the sea floor worldwide. Our study of neritic sections in Egypt shows that in the southern shallow Tethys, a prominent long-term change in bottom-water chemistry, sedimentation, and benthic foraminifera fauna was initiated at the time when the deep-sea benthic extinction event (BEE) took place. Bottom-water δ13C values on the Tethyan shelf show a sudden 3.0‰ negative shift at this event; however, contrary to the deep sea, in which the δ13C excursion was of short duration, Tethyan δ13C values did not fully return to preboundary values, but remained depressed by ˜1.5‰ for at least 1 m.y. The δ13C values at the Egyptian shelf during the BEE are much lower than would be expected if this was a source region for global deep water. The δ18O values indicate no significant change in bottom-water salinity or temperature at the BEE. The long-lasting environmental changes that began on the Egyptian shelf at the BEE may be related to, for example, gateway reorganization along the Tethyan seaway. Paleogeographic changes possibly also triggered a change in the loci of global deep-water formation; however, these loci must be sought in another part of the Tethys.

Importance of the Gulf of Aqaba for the formation of bottom water in the Red Sea

NASA Astrophysics Data System (ADS)

Plähn, Olaf; Baschek, Burkard; Badewien, Thomas H.; Walter, Maren; Rhein, Monika

2002-08-01

Conductivity-temperature-depth tracer and direct current measurements collected in the northern Red Sea in February and March 1999 are used to study the formation of deep and bottom water in that region. Historical data showed that open ocean convection in the Red Sea can contribute to the renewal of intermediate or deep water but cannot ventilate the bottom water. The observations in 1999 showed no evidence for open ocean convection in the Red Sea during the winter 1998/1999. The overflow water from the Gulf of Aqaba was found to be the densest water mass in the northern Red Sea. An anomaly of the chlorofluorocarbon component CFC-12 observed in the Gulf of Aqaba and at the bottom of the Red Sea suggests a strong contribution of this water mass to the renewal of bottom water in the Red Sea. The CFC data obtained during this cruise are the first available for this region. Because of the new signal, it is possible for the first time to subdivide the deep water column into deep and bottom water in the northern Red Sea. The available data set also shows that the outflow water from the Gulf of Suez is not dense enough to reach down to the bottom of the Red Sea but was found about 250 m above the bottom.

Weak wind-wave/tide interaction over fixed and moveable bottoms: a formulation and some preliminary results

NASA Astrophysics Data System (ADS)

Kagan, B. A.; Alvarez, O.; Izquierdo, A.

2005-05-01

The formulation of weak wind-wave/low-frequency current interaction is discussed comprehensively as applied to fixed- and moveable-bottom cases. It involves (1) a dependence of the drag coefficient on the ratio between wave and current bottom friction velocity amplitudes, (2) the resistance law for the oscillatory, rough, turbulent bottom boundary layer (BBL) which accounts for the usually neglected effects of rotation and the phase difference between the bottom stress and the friction-free current velocity, (3) the expression for the BBL depth in terms of the bottom Rossby number and (4) the bottom roughness predictor of Grant and Madsen (J. Geophys. Res., 87 (1982) 469) in the version of Tolman (J. Phys. Oceanogr., 24 (1994) 994). The formulation is implemented in the UCA (University of Cadiz) 2D nonlinear, high-resolution, hydrodynamic model and used to study the influence of wind-wave/tide interaction, bottom mobility and the improved flow-resistance description on the M 2 tidal dynamics of Cadiz Bay. The inclusion of either of the first two factors can cause the drag coefficient to increase significantly over its reference value. If the third factor is included, changes in the drag coefficient are quite moderate. This is because the effect of rotation is opposite in sign to the effect of phase difference, so that these effects taken together very nearly balance. The reason why bottom mobility has such an important influence on shallow-water tidal dynamics as wind-wave/tide interaction has, is the occurrence of the large irregular variations in the drag coefficient that accompany sediment motion.

Assessing the performance of wave breaking parameterizations in shallow waters in spectral wave models

NASA Astrophysics Data System (ADS)

Lin, Shangfei; Sheng, Jinyu

2017-12-01

Depth-induced wave breaking is the primary dissipation mechanism for ocean surface waves in shallow waters. Different parametrizations were developed for parameterizing depth-induced wave breaking process in ocean surface wave models. The performance of six commonly-used parameterizations in simulating significant wave heights (SWHs) is assessed in this study. The main differences between these six parameterizations are representations of the breaker index and the fraction of breaking waves. Laboratory and field observations consisting of 882 cases from 14 sources of published observational data are used in the assessment. We demonstrate that the six parameterizations have reasonable performance in parameterizing depth-induced wave breaking in shallow waters, but with their own limitations and drawbacks. The widely-used parameterization suggested by Battjes and Janssen (1978, BJ78) has a drawback of underpredicting the SWHs in the locally-generated wave conditions and overpredicting in the remotely-generated wave conditions over flat bottoms. The drawback of BJ78 was addressed by a parameterization suggested by Salmon et al. (2015, SA15). But SA15 had relatively larger errors in SWHs over sloping bottoms than BJ78. We follow SA15 and propose a new parameterization with a dependence of the breaker index on the normalized water depth in deep waters similar to SA15. In shallow waters, the breaker index of the new parameterization has a nonlinear dependence on the local bottom slope rather than the linear dependence used in SA15. Overall, this new parameterization has the best performance with an average scatter index of ∼8.2% in comparison with the three best performing existing parameterizations with the average scatter index between 9.2% and 13.6%.

The history and future trends of ocean warming-induced gas hydrate dissociation in the SW Barents Sea

NASA Astrophysics Data System (ADS)

Vadakkepuliyambatta, Sunil; Chand, Shyam; Bünz, Stefan

2017-01-01

The Barents Sea is a major part of the Arctic where the Gulf Stream mixes with the cold Arctic waters. Late Cenozoic uplift and glacial erosion have resulted in hydrocarbon leakage from reservoirs, evolution of fluid flow systems, shallow gas accumulations, and hydrate formation throughout the Barents Sea. Here we integrate seismic data observations of gas hydrate accumulations along with gas hydrate stability modeling to analyze the impact of warming ocean waters in the recent past and future (1960-2060). Seismic observations of bottom-simulating reflectors (BSRs) indicate significant thermogenic gas input into the hydrate stability zone throughout the SW Barents Sea. The distribution of BSR is controlled primarily by fluid flow focusing features, such as gas chimneys and faults. Warming ocean bottom temperatures over the recent past and in future (1960-2060) can result in hydrate dissociation over an area covering 0.03-38% of the SW Barents Sea.

The Secret of the Svalbard Sea Ice Barrier

NASA Technical Reports Server (NTRS)

Nghiem, Son V.; Van Woert, Michael L.; Neumann, Gregory

2004-01-01

An elongated sea ice feature called the Svalbard sea ice barrier rapidly formed over an area in the Barents Sea to the east of Svalbard posing navigation hazards. The secret of its formation lies in the bottom bathymetry that governs the distribution of cold Arctic waters masses, which impacts sea ice growth on the water surface.

Influence of aerosol estimation on coastal water products retrieved from HICO images

NASA Astrophysics Data System (ADS)

Patterson, Karen W.; Lamela, Gia

2011-06-01

The Hyperspectral Imager for the Coastal Ocean (HICO) is a hyperspectral sensor which was launched to the International Space Station in September 2009. The Naval Research Laboratory (NRL) has been developing the Coastal Water Signatures Toolkit (CWST) to estimate water depth, bottom type and water column constituents such as chlorophyll, suspended sediments and chromophoric dissolved organic matter from hyperspectral imagery. The CWST uses a look-up table approach, comparing remote sensing reflectance spectra observed in an image to a database of modeled spectra for pre-determined water column constituents, depth and bottom type. In order to successfully use this approach, the remote sensing reflectances must be accurate which implies accurately correcting for the atmospheric contribution to the HICO top of the atmosphere radiances. One tool the NRL is using to atmospherically correct HICO imagery is Correction of Coastal Ocean Atmospheres (COCOA), which is based on Tafkaa 6S. One of the user input parameters to COCOA is aerosol optical depth or aerosol visibility, which can vary rapidly over short distances in coastal waters. Changes to the aerosol thickness results in changes to the magnitude of the remote sensing reflectances. As such, the CWST retrievals for water constituents, depth and bottom type can be expected to vary in like fashion. This work is an illustration of the variability in CWST retrievals due to inaccurate aerosol thickness estimation during atmospheric correction of HICO images.

Dynamics of the Sediment Plume Over the Yangtze Bank in the Yellow and East China Seas

NASA Astrophysics Data System (ADS)

Luo, Zhifa; Zhu, Jianrong; Wu, Hui; Li, Xiangyu

2017-12-01

A distinct sediment plume exists over the Yangtze Bank in the Yellow and East China Seas (YECS) in winter, but it disappears in summer. Based on satellite color images, there are two controversial viewpoints about the formation mechanism for the sediment plume. One viewpoint is that the sediment plume forms because of cross-shelf sediment advection of highly turbid water along the Jiangsu coast. The other viewpoint is that the formation is caused by local bottom sediment resuspension and diffused to the surface layer through vertical turbulent mixing. The dynamic mechanism of the sediment plume formation has been unclear until now. This issue was explored by using a numerical sediment model in the present paper. Observed wave, current, and sediment data from 29 December 2016 to 16 January 2017 were collected near the Jiangsu coast and used to validate the model. The results indicated that the model can reproduce the hydrodynamic and sediment processes. Numerical experiments showed that the bottom sediment could be suspended by the bottom shear stress and diffuse to the surface layer by vertical mixing in winter; however, the upward diffusion is restricted by the strong stratification in summer. The sediment plume is generated locally due to bottom sediment resuspension primarily via tide-induced bottom shear stress rather than by cross-shelf sediment advection over the Yangtze Bank.

Bottom friction optimization for a better barotropic tide modelling

NASA Astrophysics Data System (ADS)

Boutet, Martial; Lathuilière, Cyril; Son Hoang, Hong; Baraille, Rémy

2015-04-01

At a regional scale, barotropic tides are the dominant source of variability of currents and water heights. A precise representation of these processes is essential because of their great impacts on human activities (submersion risks, marine renewable energies, ...). Identified sources of error for tide modelling at a regional scale are the followings: bathymetry, boundary forcing and dissipation due to bottom friction. Nevertheless, bathymetric databases are nowadays known with a good accuracy, especially over shelves, and global tide models performances are better than ever. The most promising improvement is thus the bottom friction representation. The method used to estimate bottom friction is the simultaneous perturbation stochastic approximation (SPSA) which consists in the approximation of the gradient based on a fixed number of cost function measurements, regardless of the dimension of the vector to be estimated. Indeed, each cost function measurement is obtained by randomly perturbing every component of the parameter vector. An important feature of SPSA is its relative ease of implementation. In particular, the method does not require the development of tangent linear and adjoint version of the circulation model. Experiments are carried out to estimate bottom friction with the HYbrid Coordinate Ocean Model (HYCOM) in barotropic mode (one isopycnal layer). The study area is the Northeastern Atlantic margin which is characterized by strong currents and an intense dissipation. Bottom friction is parameterized with a quadratic term and friction coefficient is computed with the water height and the bottom roughness. The latter parameter is the one to be estimated. Assimilated data are the available tide gauge observations. First, the bottom roughness is estimated taking into account bottom sediment natures and bathymetric ranges. Then, it is estimated with geographical degrees of freedom. Finally, the impact of the estimation of a mixed quadratic/linear friction is evaluated.

Basal hydraulic conditions of Ice Stream B

NASA Technical Reports Server (NTRS)

Engelhardt, Hermann; Kamb, Barclay

1993-01-01

Fifteen boreholes have been drilled to the base of Ice Stream B in the vicinity of UpB Camp. The boreholes are spread over an area of about 500 x 1000 m. Several till cores were retrieved from the bottom of the 1000-m-deep holes. Laboratory tests using a simple shear box revealed a yield strength of basal till of 2 kPa. This agrees well with in-situ measurements using a shear vane. Since the average basal shear stress of Ice Stream B with a surface slope of 0.1 degree is about 20 kPa, the ice stream cannot be supported by till that weak. Additional support for this conclusion comes from the basal water pressure that has been measured in all boreholes as soon as the hot water drill reached bottom. In several boreholes, the water pressure has been continuously monitored; in two of them, over several years. The water pressure varies but stays within 1 bar of flotation where ice overburden pressure and water pressure are equal. The ratio of water and overburden pressure lies between 0.986 and 1.002. This is an extremely high value as compared to other fast-moving ice masses; e.g., Variegated Glacier in surge has a ratio of 0.8, and Columbia Glacier - a fast-moving tidewater glacier - has a ratio of 0.9. It implies that water flow under the glacier occurs in a thin film and not in conduits that would drain away water too rapidly. It also implies that basal sliding must be very effective. Water flow under the glacier was measured in a salt-injection experiment where a salt pulse was released at the bottom of a borehole while 60 m down-glacier, the electrical resistance was measured between two other boreholes. A flow velocity of 7 mm/s was obtained.

Lake responses following lanthanum-modified bentonite clay (Phoslock®) application: an analysis of water column lanthanum data from 16 case study lakes.

PubMed

Spears, Bryan M; Lürling, Miquel; Yasseri, Said; Castro-Castellon, Ana T; Gibbs, Max; Meis, Sebastian; McDonald, Claire; McIntosh, John; Sleep, Darren; Van Oosterhout, Frank

2013-10-01

Phoslock(®) is a lanthanum (La) modified bentonite clay that is being increasingly used as a geo-engineering tool for the control of legacy phosphorus (P) release from lake bed sediments to overlying waters. This study investigates the potential for negative ecological impacts from elevated La concentrations associated with the use of Phoslock(®) across 16 case study lakes. Impact-recovery trajectories associated with total lanthanum (TLa) and filterable La (FLa) concentrations in surface and bottom waters were quantified over a period of up to 60 months following Phoslock(®) application. Both surface and bottom water TLa and FLa concentrations were <0.001 mg L(-1) in all lakes prior to the application of Phoslock(®). The effects of Phoslock(®) application were evident in the post-application maximum TLa and FLa concentrations reported for surface waters between 0.026 mg L(-1)-2.30 mg L(-1) and 0.002 mg L(-1) to 0.14 mg L(-1), respectively. Results of generalised additive modelling indicated that recovery trajectories for TLa and FLa in surface and bottom waters in lakes were represented by 2nd order decay relationships, with time, and that recovery reached an end-point between 3 and 12 months post-application. Recovery in bottom water was slower (11-12 months) than surface waters (3-8 months), most probably as a result of variation in physicochemical conditions of the receiving waters and associated effects on product settling rates and processes relating to the disturbance of bed sediments. CHEAQS PRO modelling was also undertaken on 11 of the treated lakes in order to predict concentrations of La(3+) ions and the potential for negative ecological impacts. This modelling indicated that the concentrations of La(3+) ions will be very low (<0.0004 mg L(-1)) in lakes of moderately low to high alkalinity (>0.8 mEq L(-1)), but higher (up to 0.12 mg L(-1)) in lakes characterised by very low alkalinity. The effects of elevated La(3+) concentrations following Phoslock(®) applications in lakes of very low alkalinity requires further evaluation. The implications for the use of Phoslock(®) in eutrophication management are discussed. Copyright © 2013 Elsevier Ltd. All rights reserved.

Modeling of SAR signatures of shallow water ocean topography

NASA Technical Reports Server (NTRS)

Shuchman, R. A.; Kozma, A.; Kasischke, E. S.; Lyzenga, D. R.

1984-01-01

A hydrodynamic/electromagnetic model was developed to explain and quantify the relationship between the SEASAT synthetic aperture radar (SAR) observed signatures and the bottom topography of the ocean in the English Channel region of the North Sea. The model uses environmental data and radar system parameters as inputs and predicts SAR-observed backscatter changes over topographic changes in the ocean floor. The model results compare favorably with the actual SEASAT SAR observed backscatter values. The developed model is valid for only relatively shallow water areas (i.e., less than 50 meters in depth) and suggests that for bottom features to be visible on SAR imagery, a moderate to high velocity current and a moderate wind must be present.

Mapping the seafloor geology offshore of Massachusetts

USGS Publications Warehouse

Barnhardt, Walter A.; Andrews, Brian D.

2006-01-01

Geologic and bathymetric maps help us understand the evolutionary history of the Massachusetts coast and the processes that have shaped it. The maps show the distribution of bottom types (for example, bedrock, gravel, sand, mud) and water depths over large areas of the seafloor. In turn, these two fundamental parameters largely determine the species of flora and fauna that inhabit a particular area. Knowledge of bottom types and water depths provides a framework for mapping benthic habitats and managing marine resources. The need for coastal–zone mapping to inform policy and management is widely recognized as critical for mitigating hazards, creating resource inventories, and tracking environmental changes (National Research Council, 2004; U.S. Commission on Ocean Policy, 2004).

Characterization of shallow ocean sediments using the airborne electromagnetic method

NASA Technical Reports Server (NTRS)

Won, I. J.; Smits, K.

1986-01-01

Experimental airborne electromagnetic (AEM) survey data collected in Cape Cod Bay are used to derive continuous profiles of water depth, electrical depth, water conductivity, and bottom sediment conductivity. Through a few well-known empirical relationships, the conductivities are used, in turn, to derive density, porosity, sound speed, and acoustic reflectivity of the ocean bottom. A commercially available Dighem III AEM system was used for the survey without any significant modification. The helicopter-borne system operated at 385 and 7200 Hz; both were in a horizontal coplanar configuration. The interpreted profiles show good agreement with available ground truth data. Where no such data are available, the results appear to be very reasonable. Compared with the shipborne electrode array method, the AEM method can determine the necessary parameters at a much higher speed with a better lateral resolution over a wide range of water depths from 0 to perhaps 100 m. The bottom sediment conductivity that can be measured by the AEM method is closely related to physical properties of sediments, such as porosity, density, sound speed, and, indirectly, sediment types that might carry broad implications for various offshore activities.

Environmental Impact Study of the Northern Section of the Upper Mississippi River. Pool 5.

DTIC Science & Technology

1973-11-01

Prior to the 1930’s the river bottoms were primarily wooded islands separated by deep sloughs. Hundreds of lakes and ponds were scattered through the... wooded bottoms. Bay meadows and small farming areas occupied some areas on larger islands. Marshes were limited to the shores of lakes and guts...the old condition of deep sloughs and wooded islands is found. In the middle of each pool, water backs up over the islands and old hay meadows

Wind-driven export of Weddell Sea slope water

NASA Astrophysics Data System (ADS)

Meijers, A. J. S.; Meredith, M. P.; Abrahamsen, E. P.; Morales Maqueda, M. A.; Jones, D. C.; Naveira Garabato, A. C.

2016-10-01

The export of waters from the Weddell Gyre to lower latitudes is an integral component of the southern subpolar contribution to the three-dimensional oceanic circulation. Here we use more than 20 years of repeat hydrographic data on the continental slope on the northern tip of the Antarctic Peninsula and 5 years of bottom lander data on the slope at 1000 m to show the intermittent presence of a relatively cold, fresh, westward flowing current. This is often bottom-intensified between 600 and 2000 dbar with velocities of over 20 cm s-1, transporting an average of 1.5 ± 1.5 Sv. By comparison with hydrography on the continental slope within the Weddell Sea and modeled tracer release experiments we show that this slope current is an extension of the Antarctic Slope Current that has crossed the South Scotia Ridge west of Orkney Plateau. On monthly to interannual time scales the density of the slope current is negatively correlated (r > 0.6 with a significance of over 95%) with eastward wind stress over the northern Weddell Sea, but lagging it by 6-13 months. This relationship holds in both the high temporal resolution bottom lander time series and the 20+ year annual hydrographic occupations and agrees with Weddell Sea export variability observed further east. We compare several alternative hypotheses for this wind stress/export relationship and find that it is most consistent with wind-driven acceleration of the gyre boundary current, possibly modulated by eddy dynamics, and represents a mechanism by which climatic perturbations can be rapidly transmitted as fluctuations in the supply of intermediate-level waters to lower latitudes.

14 CFR 25.535 - Auxiliary float loads.

Code of Federal Regulations, 2013 CFR

2013-01-01

..., the prescribed water loads may be distributed over the float bottom to avoid excessive local loads...=coefficient of drag force, equal to 0.133; C y=coefficient of side force, equal to 0.106; K=0.8, except that...

14 CFR 25.535 - Auxiliary float loads.

Code of Federal Regulations, 2012 CFR

2012-01-01

..., the prescribed water loads may be distributed over the float bottom to avoid excessive local loads...=coefficient of drag force, equal to 0.133; C y=coefficient of side force, equal to 0.106; K=0.8, except that...

14 CFR 25.535 - Auxiliary float loads.

Code of Federal Regulations, 2011 CFR

2011-01-01

..., the prescribed water loads may be distributed over the float bottom to avoid excessive local loads...=coefficient of drag force, equal to 0.133; C y=coefficient of side force, equal to 0.106; K=0.8, except that...

14 CFR 25.535 - Auxiliary float loads.

Code of Federal Regulations, 2010 CFR

2010-01-01

..., the prescribed water loads may be distributed over the float bottom to avoid excessive local loads...=coefficient of drag force, equal to 0.133; C y=coefficient of side force, equal to 0.106; K=0.8, except that...

14 CFR 25.535 - Auxiliary float loads.

Code of Federal Regulations, 2014 CFR

2014-01-01

..., the prescribed water loads may be distributed over the float bottom to avoid excessive local loads...=coefficient of drag force, equal to 0.133; C y=coefficient of side force, equal to 0.106; K=0.8, except that...

Neodymium isotope ratios in fish debris as a tracer for a low oxygen water mass in the equatorial Pacific across the last glacial termination.

NASA Astrophysics Data System (ADS)

Reimi Sipala, M. A.; Marcantonio, F.

2017-12-01

The deep ocean has long been suggested as a potential sink of carbon during the LGM, providing storage for the drawdown of atmospheric CO2 observed in the climate record. However, the exact location, origin and pathway of this respired carbon pool remains largely unconstrained. The equatorial Pacific is an important player in the ocean biogeochemical cycling of carbon, with many researchers focusing on the changes in iron-limited systems and potential micronutrient supply changes throughout the Pleistocene glaciation. Here we attempt to isolate the role of deep water circulation changes that may be associated with changing bottom water oxygen conditions in the Central Equatorial Pacific during the last deglaciation. We measure the variability of the Nd isotopic composition of fish debris from three sites in the Central Equatorial Pacific (CEP) along a meridional transect at approximately 160° W -- 0° 28' N (ML1208-17PC), 4° 41' N (ML1208-31BB), and 7 ° 2'N (ML1208-31BB). Nd isotopic values in fish debris reflect the Nd isotopic composition of bottom water at the time of deposition and are insensitive to moderate changes in redox conditions or pore water oxygen levels. Nd isotope ratios can, therefore, be used as an effective deep-ocean water mass tracer. This work attempts to illuminate our current understanding of changes in bottom water oxygenation conditions throughout the Equatorial Pacific over the past 25 kyr. High authigenic U concentrations during peak glacial conditions have been attributed to deep-water suboxic conditions potentially associated with increased respired carbon storage. However, it is still unclear if these changes originate in the Southern Ocean, and propagate to the equatorial Pacific through an increased in penetration of Southern Ocean Intermediate water, or if they represent a change in the efficiency of the biological pump, permitting a drawdown of oxygen in bottom water without increased nutrient availability.

Using multiple gears to assess acoustic detectability and biomass of fish species in lake superior

USGS Publications Warehouse

Yule, D.L.; Adams, J.V.; Stockwell, J.D.; Gorman, O.T.

2007-01-01

Recent predator demand and prey supply studies suggest that an annual daytime bottom trawl survey of Lake Superior underestimates prey fish biomass. A multiple-gear (acoustics, bottom trawl, and midwater trawl) nighttime survey has been recommended, but before abandoning a long-term daytime survey the effectiveness of night sampling of important prey species must be verified. We sampled three bottom depths (30, 60, and 120 m) at a Lake Superior site where the fish community included all commercially and ecologically important species. Day and night samples were collected within 48 h at all depths during eight different periods (one new and one full moon period during both early summer and late summer to early fall over 2 years). Biomass of demersal and benthic species was higher in night bottom trawl samples than in day bottom trawl samples. Night acoustic collections showed that pelagic fish typically occupied water cooler than 15°C and light levels less than 0.001 lx. Using biomass in night bottom trawls and acoustic biomass above the bottom trawl path, we calculated an index of acoustic detectability for each species. Ciscoes Coregonus artedi, kiyis C. kiyi, and rainbow smeltOsmerus mordax left the bottom at night, whereas bloaters C. hoyi stayed nearer the bottom. We compared the biomass of important prey species estimated with two survey types: day bottom trawls and night estimates of the entire water column (bottom trawl biomass plus acoustic biomass). The biomass of large ciscoes (>200 mm) was significantly greater when measured at night than when measured during daylight, but the differences for other sizes of important species did not vary significantly by survey type. Nighttime of late summer is a period when conditions for biomass estimation are largely invariant, and all important prey species can be sampled using a multiple-gear approach.

Mg/Ca- Δ CO3porewater2- -temperature calibration for Globobulimina spp.: A sensitive paleothermometer for deep-sea temperature reconstruction

NASA Astrophysics Data System (ADS)

Weldeab, Syee; Arce, Adam; Kasten, Sabine

2016-03-01

Existing benthic foraminiferal Mg/Ca-temperature calibrations are surrounded by substantial uncertainties mainly due to low temperature sensitivity of Mg/Ca in most benthic foraminifers and the effect of carbonate ion concentration on benthic foraminiferal Mg/Ca. Here we present Mg/Ca analysis of Rose Bengal stained and exceptionally well-preserved tests of the infaunal benthic foraminifer Globobulimina spp. from 39 eastern equatorial Atlantic core top samples. Mg/Ca in Globobulimina spp. varies between 2.5 mmol/mol and 9.1 mmol/mol corresponding to bottom water temperatures (BWT) between 1.8 °C and 19.1 °C and Δ CO3pore water2- between 33.7 ± 4 and - 34.3 ± 4 μmol /kg in sediment depths between 1 and 10 cm. Mg/Ca and BWT are linearly correlated with a best fit of Mg/Ca [mmol/mol] = (0.36 ± 0.02) * BWT [°C] + 2.22 ± 0.19 (r2 = 0.92, p-value: 11 *10-20, and n = 39). Using total alkalinity and pH data of pore water samples from 64 Atlantic multi-corer sites, we obtained Δ CO3pore water2- data from the depth habitat range of Globobulimina spp. (≥1 cm ≤ 10 cm below sediment surface). We show that Δ CO3pore waterSUP>2- is significantly lower than and linearly co-varies with the ΔCO2-3 of the overlying bottom water: Δ CO3pore water2- = (0.67 ± 0.05) * Δ CO3bottom water2- - (39.84 ± 1.98); r2 = 0.75, p-value: 6 *10-20, n = 64. We found a Mg/Ca sensitivity of 0.009 ± 0.0044 mmol /mol per μmol/kg Δ CO3pore water2- and Mg/Ca temperature sensitivity of 0.32 ± 0.06 mmol /mol / °C after a correction for the Δ CO3pore water2- effect. This study provides a robust Mg/Ca-temperature calibration, highlights that Δ CO3pore water2- is spatially and most likely temporally variable, and contradicts the notion that infaunal foraminiferal Mg/Ca is relatively immune from ΔCO2-3 changes in the overlying bottom water. Furthermore, comparison of down core Mg/Ca data of Cibicides pachyderma and Globobulimina spp. demonstrates that the high temperature sensitivity of Mg/Ca in Globobulimina spp. presents a more robust paleothermometer to reconstruct past changes in the thermal state of the deep ocean.

Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean

PubMed Central

Menezes, Viviane V.; Macdonald, Alison M.; Schatzman, Courtney

2017-01-01

Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean. PMID:28138548

Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean.

PubMed

Menezes, Viviane V; Macdonald, Alison M; Schatzman, Courtney

2017-01-01

Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade -1 ), warmer (0.06° ± 0.01°C decade -1 ), and less dense (0.011 ± 0.002 kg/m 3 decade -1 ). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade -1 ) compared to the 0.002 ± 0.001 kg/g decade -1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean.

An Analysis Model for Water Cone Subsidence in Bottom Water Drive Reservoirs

NASA Astrophysics Data System (ADS)

Wang, Jianjun; Xu, Hui; Wu, Shucheng; Yang, Chao; Kong, lingxiao; Zeng, Baoquan; Xu, Haixia; Qu, Tailai

2017-12-01

Water coning in bottom water drive reservoirs, which will result in earlier water breakthrough, rapid increase in water cut and low recovery level, has drawn tremendous attention in petroleum engineering field. As one simple and effective method to inhibit bottom water coning, shut-in coning control is usually preferred in oilfield to control the water cone and furthermore to enhance economic performance. However, most of the water coning researchers just have been done on investigation of the coning behavior as it grows up, the reported studies for water cone subsidence are very scarce. The goal of this work is to present an analytical model for water cone subsidence to analyze the subsidence of water cone when the well shut in. Based on Dupuit critical oil production rate formula, an analytical model is developed to estimate the initial water cone shape at the point of critical drawdown. Then, with the initial water cone shape equation, we propose an analysis model for water cone subsidence in bottom water reservoir reservoirs. Model analysis and several sensitivity studies are conducted. This work presents accurate and fast analytical model to perform the water cone subsidence in bottom water drive reservoirs. To consider the recent interests in development of bottom drive reservoirs, our approach provides a promising technique for better understanding the subsidence of water cone.

Hamiltonian models for the propagation of irrotational surface gravity waves over a variable bottom

NASA Astrophysics Data System (ADS)

Compelli, A.; Ivanov, R.; Todorov, M.

2017-12-01

A single incompressible, inviscid, irrotational fluid medium bounded by a free surface and varying bottom is considered. The Hamiltonian of the system is expressed in terms of the so-called Dirichlet-Neumann operators. The equations for the surface waves are presented in Hamiltonian form. Specific scaling of the variables is selected which leads to approximations of Boussinesq and Korteweg-de Vries (KdV) types, taking into account the effect of the slowly varying bottom. The arising KdV equation with variable coefficients is studied numerically when the initial condition is in the form of the one-soliton solution for the initial depth. This article is part of the theme issue 'Nonlinear water waves'.

Properties of the water column and bottom derived from Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data

NASA Astrophysics Data System (ADS)

Lee, Zhongping; Carder, Kendall L.; Chen, Robert F.; Peacock, Thomas G.

2001-06-01

Using Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data as an example, we show in this study that the properties of the water column and bottom of a large, shallow area can be adequately retrieved using a model-driven optimization technique. The simultaneously derived properties include bottom depth, bottom albedo, and water absorption and backscattering coefficients, which in turn could be used to derive concentrations of chlorophyll, dissolved organic matter, and suspended sediments in the water column. The derived bottom depths were compared with a bathymetry chart and a boat survey and were found to agree very well. Also, the derived bottom albedo image shows clear spatial patterns, with end-members consistent with sand and seagrass. The image of absorption and backscattering coefficients indicates that the water is quite horizontally mixed. Without bottom corrections, chlorophyll a retrievals were ˜50 mg m-3, while the retrievals after bottom corrections were tenfold less, approximating real values. These results suggest that the model and approach used work very well for the retrieval of subsurface properties of shallow-water environments even for rather turbid environments like Tampa Bay, Florida.

Development of the benethic nepheloid layer on the south Texas continental shelf, western Gulf of Mexico

USGS Publications Warehouse

Shideler, G.L.

1981-01-01

A monitoring study of suspended sediment on the South Texas Continental Shelf indicates that a turbid benthic nepheloid layer is regionally persistent. A sequence of quasi-synoptic measurements of the water column obtained during six cruises in an 18-month period indicates substantial spatial and temporal variability in nepheloidlayer characteristics. Regionally, the thickness of the shelf nepheloid layer increases both seaward and in a convergent alongshelf direction. Greatest thicknesses occur over a muddy substrate, indicating a causal relationship; maximum observed local thickness is 35 m which occurs along the southern shelf break. Analyses of suspended particulate matter in shelf bottom waters indicate mean concentrations ranging from 49 ?? 104 to 111 ?? 104 particle counts/cc; concentrations persistently increase shoreward throughout the region. Bottom particulate matter is predominantly composed of inorganic detritus. Admixtures of organic skeletal particles, primarily diatoms, are generally present but average less than 10% of the total particulate composition. Texturally, the particulate matter in bottom waters is predominantly poorly sorted sediment composed of very fine silt (3.9-7.8 ??m). The variability in nepheloid-layer characteristics indicates a highly dynamic shelf feature. The relationship of nepheloid-layer characteristics to hydrographic and substrate conditions suggests a conceptual model whereby nepheloid-layer development and maintenance are the results of the resuspension of sea-floor sediment. Bottom turbulence is attributed primarily to vertical shear and shoaling progressive internal waves generated by migrating shelf-water masses, especially oceanic frontal systems, and secondarily to shoaling surface gravity waves. ?? 1981.

Determination of water depth with high-resolution satellite imagery over variable bottom types

USGS Publications Warehouse

Stumpf, Richard P.; Holderied, Kristine; Sinclair, Mark

2003-01-01

A standard algorithm for determining depth in clear water from passive sensors exists; but it requires tuning of five parameters and does not retrieve depths where the bottom has an extremely low albedo. To address these issues, we developed an empirical solution using a ratio of reflectances that has only two tunable parameters and can be applied to low-albedo features. The two algorithms--the standard linear transform and the new ratio transform--were compared through analysis of IKONOS satellite imagery against lidar bathymetry. The coefficients for the ratio algorithm were tuned manually to a few depths from a nautical chart, yet performed as well as the linear algorithm tuned using multiple linear regression against the lidar. Both algorithms compensate for variable bottom type and albedo (sand, pavement, algae, coral) and retrieve bathymetry in water depths of less than 10-15 m. However, the linear transform does not distinguish depths >15 m and is more subject to variability across the studied atolls. The ratio transform can, in clear water, retrieve depths in >25 m of water and shows greater stability between different areas. It also performs slightly better in scattering turbidity than the linear transform. The ratio algorithm is somewhat noisier and cannot always adequately resolve fine morphology (structures smaller than 4-5 pixels) in water depths >15-20 m. In general, the ratio transform is more robust than the linear transform.

76 FR 49737 - Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-11

... stock(s) for subsistence uses (where relevant). The authorization must set forth the permissible methods... shooting a test pattern over an ocean bottom instrument in shallow water. This method is neither practical nor valid in water depths as great as 3,000 m (9,842.5 ft). The alternative method of conducting site...

Deep and bottom water export from the Southern Ocean to the Pacific over the past 38 million years

USGS Publications Warehouse

van de Flierdt, T.; Frank, M.; Halliday, A.N.; Hein, J.R.; Hattendorf, B.; Gunther, D.; Kubik, P.W.

2004-01-01

The application of radiogenic isotopes to the study of Cenozoic circulation patterns in the South Pacific Ocean has been hampered by the fact that records from only equatorial Pacific deep water have been available. We present new Pb and Nd isotope time series for two ferromanganese crusts that grew from equatorial Pacific bottom water (D137-01, "Nova," 7219 m water depth) and southwest Pacific deep water (63KD, "Tasman," 1700 m water depth). The crusts were dated using 10Be/9Be ratios combined with constant Co-flux dating and yield time series for the past 38 and 23 Myr, respectively. The surface Nd and Pb isotope distributions are consistent with the present-day circulation pattern, and therefore the new records are considered suitable to reconstruct Eocene through Miocene paleoceanography for the South Pacific. The isotope time series of crusts Nova and Tasman suggest that equatorial Pacific deep water and waters from the Southern Ocean supplied the dissolved trace metals to both sites over the past 38 Myr. Changes in the isotopic composition of crust Nova are interpreted to reflect development of the Antarctic Circumpolar Current and changes in Pacific deep water circulation caused by the build up of the East Antarctic Ice Sheet. The Nd isotopic composition of the shallower water site in the southwest Pacific appears to have been more sensitive to circulation changes resulting from closure of the Indonesian seaway. Copyright 2004 by the American Geophysical Union.

Does water level affect benthic macro-invertebrates of a marginal lake in a tropical river-reservoir transition zone?

PubMed

Zerlin, R A; Henry, R

2014-05-01

Benthic macro-invertebrates are important components of freshwater ecosystems which are involved in ecological processes such as energy transfer between detritus and consumers and organic matter recycling. The aim of this work was to investigate the variation in organism richness, diversity and density of benthic fauna during the annual cycle in Camargo Lake, a lake marginal to Paranapanema River, southeast Brazil. The correlation of environmental factors with community attributes of the macro-benthic fauna was assessed. Since Camargo Lake is connected to the river, we tested the hypothesis that water level variation is the main regulating factor of environmental variables and of the composition and abundance of benthic macro-invertebrates. The results indicated that lake depth varied with rainfall, being the highest at the end of the rising water period and the lowest at the beginning of this period. The sediment granulometry was more heterogeneous at the bottom of the lake by the end of the high water period. The benthic macro-invertebrate fauna was composed by 15 taxa. The Diptera order was represented by seven taxa and had greater richness in relation to other taxa. This group was responsible for 60% of the total abundance of organisms, followed by Ephemeroptera (22%) and Anellida (16%). Significant differences were observed over time in total richness and, in density of Narapa bonettoi, Chaoborus, Ablabesmyia gr. annulata, Chironomus gigas, Larsia fittkau, and Procladius sp. 2. Total taxa richness correlated negatively with water pH, transparency, conductivity, and bottom water oxygen. Higher positive correlations were found between the densities of some taxa and bottom water oxygen, conductivity and very fine sand, silt + clay of sediment, while negative correlations were recorded with organic matter, and fine, medium and coarse sand, bottom water temperature, mean temperature and rainfall. The significant temporal difference in water level was associated with changes in abiotic factors and macro-invertebrate community attributes.

Near-surface enrichment of zooplankton over a shallow back reef: implications for coral reef food webs

NASA Astrophysics Data System (ADS)

Alldredge, A. L.; King, J. M.

2009-12-01

Zooplankton were 3-8 times more abundant during the day near the surface than elsewhere in the water column over a 1-2.4 m deep back reef in Moorea, French Polynesia. Zooplankton were also significantly more abundant near the surface at night although gradients were most pronounced under moonlight. Zooplankton in a unidirectional current became concentrated near the surface within 2 m of departing a well-mixed trough immediately behind the reef crest, indicating that upward swimming behavior, rather than near-bottom depletion by reef planktivores, was the proximal cause of these gradients. Zooplankton were highly enriched near the surface before and after a full lunar eclipse but distributed evenly throughout the water column during the eclipse itself supporting light as a proximal cue for the upward swimming behavior of many taxa. This is the first investigation of the vertical distribution of zooplankton over a shallow back reef typical of island barrier reef systems common around the world. Previous studies on deeper fringing reefs found zooplankton depletion near the bottom but no enrichment aloft. In Moorea, where seawater is continuously recirculated out the lagoon and back across the reef crest onto the back reef, selection for upward swimming behavior may be especially strong, because the surface serves both as a refuge from predation and an optimum location for retention within the reef system. Planktivorous fish and corals that can forage or grow even marginally higher in the water column might have a substantial competitive advantage over those nearer the bottom on shallow reefs. Zooplankton abundance varied more over a few tens of centimeters vertical distance than it did between seasons or even between day and night indicating that great care must be taken to accurately assess the availability of zooplankton as food on shallow reefs.

Sources of Arctic Ocean upper halocline and changes in its properties

NASA Astrophysics Data System (ADS)

Anderson, L. G.; Andersson, P. S.; Bjvrk, G. M.; Jutterstrom, S.; Wahlstrom, I.

2011-12-01

The upper halocline of the Arctic Ocean has a distinct chemical signature by its high nutrient and partial pressure of carbon dioxide as well as low oxygen and pH values. This signature is formed along the bottoms of the Siberian shelf seas, primarily the Chukchi and East Siberian Seas, by a combination of mineralization of organic matter and release of the decay products to the sea ice brine enriched bottom water. In this contribution we use salinity and total alkalinity data to show that the fraction of sea ice brine in the nutrient enriched upper halocline water in the central Arctic Ocean is up to 4%. This water of low pH, and thus also low in calcium carbonate solubility, is found between about 100 and 200 m depth and is thus close to the productive surface water in a future central Arctic Ocean of less summer sea ice cover. In the East Siberian Sea the bottom waters with exceptional high nutrient concentration and low pH have typically between 5 and 10% of sea ice brine as computed form salinity and oxygen-18 vales. On the continental slope, over bottom depths of 15-200 m, the brine contribution was 6% at the nutrient maximum depth (50-100 m). At the same location as well as over deeper waters the silicate maximum was found over a wider salinity range than traditionally, in agreement with observations of Nishino et al (J. Oceanogr, Vol. 65, pp. 871 to 883, 2009) in the area of the deep Arctic Ocean east of the Chukchi Plateau. However, the water with lowest salinity (~32.5) in the silicate maximum had maximum in nitrate deficit expressed as N** (= [NO3] - 16[PO4] + 2.9) and the waters with highest salinity (~34.5) had the lowest oxygen concentration. This pattern is not obvious and point to at least two different biochemical environments within the East Siberian Sea that has not been observed before and could be a sign of a changing marine climate in the East Siberian Sea. One cause could be more open water in the summer season followed by more sea ice formation and brine production in the fall/winter. Strong signals of sea ice brine was also observed in the nutrient rich water found in the Herald Valley of the Chukchi Sea. This water is likely flowing north and has traditionally been assumed to be a significant contributor to the upper halocline in the central Arctic Ocean. A challenging question for the future is; are changing sea ice conditions and biogeochemical processes on the Siberian shelves impacting the composition of the halocline of the central Arctic Ocean. A follow up issue is then what effect this might have on the ecosystem of these waters.

Evidence of Enhanced Respired Carbon in Eastern Equatorial Pacific Deep-Waters over the last 30,000 years

NASA Astrophysics Data System (ADS)

Umling, N. E.; Thunell, R.

2016-12-01

Rapid decreases in glacial deep water reservoir ages have been observed in the Eastern Equatorial Pacific (EEP; this study), North Pacific (Rae et al., 2014), Southwest Pacific (Sikes et al., 2016), and North Atlantic (Skinner et al., 2013). It has been hypothesized that release of a deep ocean 14C-depleted, respired-carbon reservoir to the surface ocean and atmosphere is the most likely mechanism for the observed increases in atmospheric CO2 concentrations recorded in ice cores during the last glacial-interglacial transition (Broecker and Barker, 2007). This study examines whether oxygenation, organic carbon flux, and carbonate chemistry in the EEP deep-waters reflect an increase in respired carbon associated with recorded 14C-depletions using isotopic and trace element records from three Panama Basin cores (2,650-3,200 m water-depth). An increase in glacial deep-water respired carbon storage would result in a shift of DIC speciation towards lower carbonate ion concentrations along with deoxygenation of bottom waters. Specifically, we use the boron to calcium (B/Ca) and uranium to calcium (U/Ca) ratios of the benthic foraminifera Cibicidoides wuellerstorfi to reconstruct deep-water carbonate ion concentration (Yu and Elderfield, 2007; Raizsch et al., 2011). Additionally, bottom water oxygenation is estimated from the difference in δ13C of benthic foraminifera living in pore waters at the anoxic boundary and of those living in bottom water (Δ δ13C; Hoogakker et al., 2015, 2016), while carbon flux was assessed from the U/Ca and Cd/Ca of foraminiferal authigenic coatings.

PAH and PCB in the Baltic -- A budget approach including fluxes, occurrence and concentration variability in air, suspended and settling particulates in water, surface sediments and river water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broman, D.; Axelman, J.; Bandh, C.

In order to study the fate and occurrence of two groups of hydrophobic compounds in the Baltic aquatic environment a large number of samples were collected from the southern Baltic proper to the northern Bothnian Bay for the analyses of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). The following sample matrices were collected; bottom surface sediments (0--1 cm, collected with gravity corer), settling particulate matter (collected with sediment traps), open water samples and over water samples (suspended particulates and dissolved fraction sampled by filtration) and air samples (aerosols and vapor phase sampled by filtration). All samples (except over watermore » and air) were collected at open sea in the Baltic. The analyses results have been used to make a model approach on the whole Baltic and to elucidate different aspects of the behavior of PAHs and PCBs in the Baltic, such as the occurrence of the compounds in water and sediment, the total content as well as the concentration variabilities over such a large geographical area, Further, the data on settling particulate matter as well as the air concentration data were used to estimate the total fluxes of PAHs and PCBs to the bottoms of the Baltic and t o the total water area of the Baltic, respectively. Further, data on the PAH and PCB content in river water from four major rivers provides rough estimates of the riverine input to the Baltic. The dynamics of PAHs and PCBs within the water mass have also been studied in terms of settling velocities and residence times in the water mass for these type of compounds in the open Baltic.« less

When Big Ice Turns Into Water It Matters For Houses, Stores And Schools All Over

NASA Astrophysics Data System (ADS)

Bell, R. E.

2017-12-01

When ice in my glass turns to water it is not bad but when the big ice at the top and bottom of the world turns into water it is not good. This new water makes many houses, stores and schools wet. It is really bad during when the wind is strong and the rain is hard. New old ice water gets all over the place. We can not get to work or school or home. We go to the big ice at the top and bottom of the world to see if it will turn to water soon and make more houses wet. We fly over the big ice to see how it is doing. Most of the big ice sits on rock. Around the edge of the big sitting on rock ice, is really low ice that rides on top of the water. This really low ice slows down the big rock ice turning into water. If the really low ice cracks up and turns into little pieces of ice, the big rock ice will make more houses wet. We look to see if there is new water in the cracks. Water in the cracks is bad as it hurts the big rock ice. Water in the cracks on the really low ice will turn the low ice into many little pieces of ice. Then the big rock ice will turn to water. That is water in cracks is bad for the houses, schools and businesses. If water moves off the really low ice, it does not stay in the cracks. This is better for the really low ice. This is better for the big rock ice. We took pictures of the really low ice and saw water leaving. The water was not staying in the cracks. Water leaving the really low ice might be good for houses, schools and stores.

Properties of the Water Column and Bottom Derived from AVIRIS Data

NASA Technical Reports Server (NTRS)

Lee, Zhong-Ping; Carder, Kendall L.; Chen, F. Robert; Peacock, Thomas G.

2001-01-01

Using AVIRIS data as an example, we show in this study that the optical properties of the water column and bottom of a large, shallow area can be adequately retrieved using a model-driven optimization technique. The simultaneously derived properties include bottom depth, bottom albedo, and water absorption and backscattering coefficients, which in turn could be used to derive concentrations of chlorophyll, dissolved organic matter, and suspended sediments. The derived bottom depths were compared with a bathymetry chart and a boat survey and were found to agree very well. Also, the derived bottom-albedo image shows clear spatial patterns, with end members consistent with sand and seagrass. The image of absorption and backscattering coefficients indicates that the water is quite horizontally mixed. These results suggest that the model and approach used work very well for the retrieval of sub-surface properties of shallow-water environments even for rather turbid environments like Tampa Bay, Florida.

Bottom sediment as a source of organic contaminants in Lake Mead, Nevada, USA

USGS Publications Warehouse

Alvarez, David A.; Rosen, Michael R.; Perkins, Stephanie D.; Cranor, Walter L.; Schroeder, Vickie L.; Jones-Lepp, Tammy L.

2012-01-01

Treated wastewater effluent from Las Vegas, Nevada and surrounding communities' flow through Las Vegas Wash (LVW) into the Lake Mead National Recreational Area at Las Vegas Bay (LVB). Lake sediment is a likely sink for many hydrophobic synthetic organic compounds (SOCs); however, partitioning between the sediment and the overlying water could result in the sediment acting as a secondary contaminant source. Locating the chemical plumes may be important to understanding possible chemical stressors to aquatic organisms. Passive sampling devices (SPMDs and POCIS) were suspended in LVB at depths of 3.0, 4.7, and 6.7 (lake bottom) meters in June of 2008 to determine the vertical distribution of SOCs in the water column. A custom sediment probe was used to also bury the samplers in the sediment at depths of 0–10, 10–20, and 20–30 cm. The greatest number of detections in samplers buried in the sediment was at the 0–10 cm depth. Concentrations of many hydrophobic SOCs were twice as high at the sediment–water interface than in the mid and upper water column. Many SOCs related to wastewater effluents, including fragrances, insect repellants, sun block agents, and phosphate flame retardants, were found at highest concentrations in the middle and upper water column. There was evidence to suggest that the water infiltrated into the sediment had a different chemical composition than the rest of the water column and could be a potential risk exposure to bottom-dwelling aquatic organisms.

In situ spectral response of the Arabian Gulf and Sea of Oman coastal waters to bio-optical properties.

PubMed

Al Shehhi, Maryam R; Gherboudj, Imen; Ghedira, Hosni

2017-10-01

Mapping of Chlorophyll-a (Chl-a) over the coastal waters of the Arabian Gulf and the Sea of Oman using the satellite-based observations, such as MODIS (Moderate Resolution Imaging Spectro-radiometer), has shown inferior performance (Chl-a overestimation) than that of deep waters. Studies in the region have shown that this poor performance is due to three reasons: (i) water turbidity (sediments re-suspension), and the presence of colored dissolved organic matter (CDOM), (ii) bottom reflectance and (iii) incapability of the existing atmospheric correction models to reduce the effect of the aerosols from the water leaving radiance. Therefore, this work focuses on investigating the sensitivity of the in situ spectral signatures of these coastal waters to the algal (chlorophyll: Chl-a), non-algal (sediments and CDOM) and the bottom reflectance properties, in absence of contributions from the atmosphere. Consequently, the collected in situ spectral signatures will improve our understanding of Arabian Gulf and Sea of Oman water properties. For this purpose, comprehensive field measurements were carried out between 2013 and 2016, over Abu-Dhabi (Arabian Gulf) and Fujairah (Sea of Oman) where unique water quality data were collected. Based on the in situ water spectral analysis, the bottom reflectance (water depth<20m) are found to degrade the performance of the conventional ocean color algorithms more than the sediment-laden waters where these waters increase the R rs at the blue and red ranges. The increasing presence of CDOM markedly decreases the R rs in the blue range, which is conflicting with the effect of Chl-a. Given the inadequate performance of the widely used ocean-color algorithms (OC3: ocean color 3, OC2: ocean color 2) in retrieving Chl-a in these very shallow coastal waters, therefore, a new algorithm is proposed here based on a 3-bands ratio approach using [R rs (656) -1 -R rs (506) -1 ]×R rs (661). The selected optimum bands (656nm, 506nm, and 661nm) from this approach can be used to retrieve the Chl-a more accurately in these coastal Case II (turbid) waters which are close to the bands of the current missions such as Sentinel-3 OLCI (Ocean and Land Colour Instrument), MODIS, VIIRS (Visible Infrared Imaging Radiometer Suite) and LandSat 8. However, more uniformly distributed data over the Arabian Gulf is required to have a highly accurate regional model for Chl-a retrieval. Copyright © 2017 Elsevier B.V. All rights reserved.

Chemical evolution of the Salton Sea, California: nutrient and selenium dynamics

USGS Publications Warehouse

Schroeder, Roy A.; Orem, William H.; Kharaka, Yousif K.

2002-01-01

The Salton Sea is a 1000-km2 terminal lake located in the desert area of southeastern California. This saline (∼44 000 mg l−1 dissolved solids) lake started as fresh water in 1905–07 by accidental flooding of the Colorado River, and it is maintained by agricultural runoff of irrigation water diverted from the Colorado River. The Salton Sea and surrounding wetlands have recently acquired substantial ecological importance because of the death of large numbers of birds and fish, and the establishment of a program to restore the health of the Sea. In this report, we present new data on the salinity and concentration of selected chemicals in the Salton Sea water, porewater and sediments, emphasizing the constituents of concern: nutrients (N and P), Se and salinity. Chemical profiles from a Salton Sea core estimated to have a sedimentation rate of 2.3 mm yr−1 show increasing concentrations of OC, N, and P in younger sediment that are believed to reflect increasing eutrophication of the lake. Porewater profiles from two locations in the Sea show that diffusion from bottom sediment is only a minor source of nutrients to the overlying water as compared to irrigation water inputs. Although loss of N and Se by microbial-mediated volatilization is possible, comparison of selected element concentrations in river inputs and water and sediments from the Salton Sea indicates that most of the N (from fertilizer) and virtually all of the Se (delivered in irrigation water from the Colorado River) discharged to the Sea still reside within its bottom sediment. Laboratory simulation on mixtures of sediment and water from the Salton Sea suggest that sediment is a potential source of N and Se to the water column under aerobic conditions. Hence, it is important that any engineered changes made to the Salton Sea for remediation or for transfer of water out of the basin do not result in remobilization of nutrients and Se from the bottom sediment into the overlying water.

Study on an undershot cross-flow water turbine

NASA Astrophysics Data System (ADS)

Nishi, Yasuyuki; Inagaki, Terumi; Li, Yanrong; Omiya, Ryota; Fukutomi, Junichiro

2014-06-01

This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water turbines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after attaching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effective head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine efficiency. Also, the runner with no bottom plate differed from runners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full rotational speed range compared with that found in runners that had a bottom plate.

Chemical data for bottom sediment, lake water, bottom-sediment pore water, and fish in Mountain Creek Lake, Dallas, Texas, 1994-96

USGS Publications Warehouse

Jones, S.A.; Van Metre, P.C.; Moring, J.B.; Braun, C.L.; Wilson, J.T.; Mahler, B.J.

1997-01-01

Mountain Creek Lake is a reservoir adjacent to two U.S. Department of the Navy facilities, the Naval Weapons Industrial Reserve Plant and the Naval Air Station in Dallas, Texas. A Resource Conservation and Recovery Act Facility Investigation found ground-water plumes containing chlorinated solvents on both facilities. These findings led to a U.S. Geological Survey study of Mountain Creek Lake adjacent to both facilities between June 1994 and August 1996. Bottom sediments, lake water, bottom-sediment pore water, and fish were collected for chemical analysis.

The characteristics and dynamics of wave-driven flow across a platform coral reef in the Red Sea

NASA Astrophysics Data System (ADS)

Lentz, S. J.; Churchill, J. H.; Davis, K. A.; Farrar, J. T.; Pineda, J.; Starczak, V.

2016-02-01

Current dynamics across a platform reef in the Red Sea near Jeddah, Saudi Arabia, are examined using 18 months of current profile, pressure, surface wave, and wind observations. The platform reef is 700 m long, 200 m across with spatial and temporal variations in water depth over the reef ranging from 0.6 to 1.6 m. Surface waves breaking at the seaward edge of the reef cause a 2-10 cm setup of sea level that drives cross-reef currents of 5-20 cm s-1. Bottom stress is a significant component of the wave setup balance in the surf zone. Over the reef flat, where waves are not breaking, the cross-reef pressure gradient associated with wave setup is balanced by bottom stress. The quadratic drag coefficient for the depth-average flow decreases with increasing water depth from Cda = 0.17 in 0.4 m of water to Cda = 0.03 in 1.2 m of water. The observed dependence of the drag coefficient on water depth is consistent with open-channel flow theory and a hydrodynamic roughness of zo = 0.06 m. A simple one-dimensional model driven by incident surface waves and wind stress accurately reproduces the observed depth-averaged cross-reef currents and a portion of the weaker along-reef currents over the focus reef and two other Red Sea platform reefs. The model indicates the cross-reef current is wave forced and the along-reef current is partially wind forced.

Ground-penetrating radar: A tool for monitoring bridge scour

USGS Publications Warehouse

Anderson, N.L.; Ismael, A.M.; Thitimakorn, T.

2007-01-01

Ground-penetrating radar (GPR) data were acquired across shallow streams and/or drainage ditches at 10 bridge sites in Missouri by maneuvering the antennae across the surface of the water and riverbank from the bridge deck, manually or by boat. The acquired two-dimensional and three-dimensional data sets accurately image the channel bottom, demonstrating that the GPR tool can be used to estimate and/or monitor water depths in shallow fluvial environments. The study results demonstrate that the GPR tool is a safe and effective tool for measuring and/or monitoring scour in proximity to bridges. The technique can be used to safely monitor scour at assigned time intervals during peak flood stages, thereby enabling owners to take preventative action prior to potential failure. The GPR tool can also be used to investigate depositional and erosional patterns over time, thereby elucidating these processes on a local scale. In certain instances, in-filled scour features can also be imaged and mapped. This information may be critically important to those engaged in bridge design. GPR has advantages over other tools commonly employed for monitoring bridge scour (reflection seismic profiling, echo sounding, and electrical conductivity probing). The tool doesn't need to be coupled to the water, can be moved rapidly across (or above) the surface of a stream, and provides an accurate depth-structure model of the channel bottom and subchannel bottom sediments. The GPR profiles can be extended across emerged sand bars or onto the shore.

76 FR 14923 - Endangered and Threatened Species; Take of Anadromous Fish

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-18

... (i.e., surface and bottom water temperature, salinity, near bottom dissolved oxygen concentration...-water and bottom trawls) are adequately characterizing schools of hake. The IVC research would take...

Characterization of bottom-sediment, water, and elutriate chemistry at selected stations at Reelfoot Lake, Tennessee

USGS Publications Warehouse

Broshears, R.E.

1991-01-01

To better-understand and predict the potential effect of dredging on water quality at Reelfoot Lake, chemical analyses were conducted on samples of lake water, bottom sediment, and elutriate water. Chemical analyses were conducted on samples of lake water, bottom sediment, and elutriate water collected at five stations in the lake during November 1988. Lake water was of the calcium magnesium bicarbonate type with an average dissolved-solids concentration of 120 milligrams per liter. Trace constituents were present in bottom sediments at concentrations representative of their average relative abundance in the earth?s crust. Elutriate waters prepared by mixing bottom sediment and lake water had suspended-solids concentrations as high as 2,000 milligrams per liter which exerted significant oxygen demand Trace constituents in the unfiltered elutriate waters were elevated with respect to lake water; elevated concentrations were attributable to the increased suspended-solids concentrations. Concentrations of total-recoverable copper, lead., and zinc in many elutriate waters exceeded U.S. Environmental Protection Agency?s water-quality criteria for the protection of freshwater aquatic life. The toxicity of elutriate waters, as measured by a 48-hour bioassay with Ceriodaphnia dubia, was low.

Re-initiation of bottom water formation in the East Sea (Japan Sea) in a warming world.

PubMed

Yoon, Seung-Tae; Chang, Kyung-Il; Nam, SungHyun; Rho, TaeKeun; Kang, Dong-Jin; Lee, Tongsup; Park, Kyung-Ae; Lobanov, Vyacheslav; Kaplunenko, Dmitry; Tishchenko, Pavel; Kim, Kyung-Ryul

2018-01-25

The East Sea (Japan Sea), a small marginal sea in the northwestern Pacific, is ventilated deeply down to the bottom and sensitive to changing surface conditions. Addressing the response of this marginal sea to the hydrological cycle and atmospheric forcing would be helpful for better understanding present and future environmental changes in oceans at the global and regional scales. Here, we present an analysis of observations revealing a slowdown of the long-term deepening in water boundaries associated with changes of water formation rate. Our results indicate that bottom (central) water formation has been enhanced (reduced) with more (less) oxygen supply to the bottom (central) layer since the 2000s. This paper presents a new projection that allows a three-layered deep structure, which retains bottom water, at least until 2040, contrasting previous results. This projection considers recent increase of slope convections mainly due to the salt supply via air-sea freshwater exchange and sea ice formation and decrease of open-ocean convections evidenced by reduced mixed layer depth in the northern East Sea, resulting in more bottom water and less central water formations. Such vigorous changes in water formation and ventilation provide certain implications on future climate changes.

Seismo-acoustic ray model benchmarking against experimental tank data.

PubMed

Camargo Rodríguez, Orlando; Collis, Jon M; Simpson, Harry J; Ey, Emanuel; Schneiderwind, Joseph; Felisberto, Paulo

2012-08-01

Acoustic predictions of the recently developed traceo ray model, which accounts for bottom shear properties, are benchmarked against tank experimental data from the EPEE-1 and EPEE-2 (Elastic Parabolic Equation Experiment) experiments. Both experiments are representative of signal propagation in a Pekeris-like shallow-water waveguide over a non-flat isotropic elastic bottom, where significant interaction of the signal with the bottom can be expected. The benchmarks show, in particular, that the ray model can be as accurate as a parabolic approximation model benchmarked in similar conditions. The results of benchmarking are important, on one side, as a preliminary experimental validation of the model and, on the other side, demonstrates the reliability of the ray approach for seismo-acoustic applications.

Hamiltonian models for the propagation of irrotational surface gravity waves over a variable bottom.

PubMed

Compelli, A; Ivanov, R; Todorov, M

2018-01-28

A single incompressible, inviscid, irrotational fluid medium bounded by a free surface and varying bottom is considered. The Hamiltonian of the system is expressed in terms of the so-called Dirichlet-Neumann operators. The equations for the surface waves are presented in Hamiltonian form. Specific scaling of the variables is selected which leads to approximations of Boussinesq and Korteweg-de Vries (KdV) types, taking into account the effect of the slowly varying bottom. The arising KdV equation with variable coefficients is studied numerically when the initial condition is in the form of the one-soliton solution for the initial depth.This article is part of the theme issue 'Nonlinear water waves'. © 2017 The Author(s).

Implementation and testing of a Deep Water Correlation Velocity Sonar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dickey, F.R.; Bookheimer, W.C.; Rhoades, K.W.

1983-05-01

The paper describes a new sonar designated the Magnavox MX 810 Deep Water Correlation Sonar which is under development by the General Electric Company and the Magnavox Advanced Products and Systems Company. The sonar measures ship's velocity relative to the bottom but instead of using the conventional doppler effect, it uses the correlation method described by Dickey and Edward in 1978. In this method, the narrow beams required for doppler are not needed and a low frequency that penetrates to the bottom in deep water is used. The sonar was designed with the constraint that it use a transducer thatmore » mounts through a single 12 inch gate valve. Most offshore geophysical surveys at present make use of an integrated navigation system with bottom referenced velocity input from a doppler sonar which, because of limitations on the sonar bottomtracking range, has difficulty in areas where the water depth is greater than about 500 meters. The MX 810 provides bottom tracking in regions of much greater water depth. It also may be applied as an aid in continuous positioning of a vessel over a fixed location. It also should prove useful as a more general navigation aid. The sonar is undergoing a series of tests using Magnavox's facilities for the purpose of verifying the performance and obtaining data to support and quantify planned improvements in both software and hardware. A prototype transducer of only 5 watts power output was used, but in spite of this low power, successful operation to depths of 1900 meters was obtained. Extrapolation to system parameters to be implemented in production models predicts operation to depths of 5000 meters.« less

Trends in polychlorinated biphenyl concentrations in Hudson River water five years after elimination of point sources

USGS Publications Warehouse

Schroeder, R.A.; Barnes, C.R.

1983-01-01

Industrial discharge of polychlorinated biphenyls (PCBs) to the Hudson River from 1950 to the mid-1970 's has resulted in serious degradation of the water. Contaminated river-bottom sediments continue to contribute PCBs to the river water. Concentrations in the sediment range from several hundred micrograms per gram near the outfall to less than 10 micrograms per gram in the lower estuary. PCBs are supplied by bottom sediments to the overlying water by two mechanisms--desorption and resuspension. Because desorption is a relatively constant process, concentrations of PCBs decrease as water discharge increases. At high flow, however, scouring by turbulence causes resuspension of PCB-laden sediment. Transport rates indicate that most PCBs enter the water from the most contaminated sediments, which are within 20 kilometers of the outfall. Mean daily transport from the upper river (except during high discharges) has decreased from 10 kilograms in 1976 to 5 kilograms in the late 1970 's and to 1 kilogram in 1981. This decrease probably results from the burial of highly contaminated sediments by cleaner sediments originating upstream. (USGS)

Temperature inverted haloclines provide winter warm-water refugia for manatees in southwest Florida

USGS Publications Warehouse

Stith, Bradley M.; Reid, James P.; Langtimm, Catherine A.; Swain, Eric D.; Doyle, Terry J.; Slone, Daniel H.; Decker, Jeremy D.; Soderqvist, Lars E.

2010-01-01

Florida manatees (Trichechus manatus latirostris) overwintering in the Ten Thousand Islands and western Everglades have no access to power plants or major artesian springs that provide warm-water refugia in other parts of Florida. Instead, hundreds of manatees aggregate at artificial canals, basins, and natural deep water sites that act as passive thermal refugia (PTR). Monitoring at two canal sites revealed temperature inverted haloclines, which provided warm salty bottom layers that generally remained above temperatures considered adverse for manatees. At the largest PTR, the warmer bottom layer disappeared unless significant salt stratification was maintained by upstream freshwater inflow over a persistent tidal wedge. A detailed three-dimensional hydrology model showed that salinity stratification inhibited vertical convection induced by atmospheric cooling. Management or creation of temperature inverted haloclines may be a feasible and desirable option for resource managers to provide passive thermal refugia for manatees and other temperature sensitive aquatic species.

Larval habitat choice in still water and flume flows by the opportunistic bivalve Mulinia lateralis

NASA Astrophysics Data System (ADS)

Grassle, Judith P.; Snelgrove, Paul V. R.; Butman, Cheryl Ann

Competent pediveligers of the coot clam Mulinia lateralis (Say) clearly preferred an organically-rich mud over abiotic glass beads in 24-h flume experiments, and often demonstrated the same choice in still-water experiments. We hypothesize that peediveligers with characteristic helical swimming paths above the bottom can exercise habitat choice in both still water nad flow, but that the limited swimming ambits of physiologically older periveligers require near-bottom flows to move the larvae between sediment patches so that they can exercise habitat choice. Although M. lateralis larvae are planktotrophic, their ability to delay metamorphosis in the absence of a preferred sediment cue is limited to about five days, a shorter time than the lecithotrophi larvae of the opportunistic polychaete species, Capitella spp. I and II. Field distributions of all three opportunistic species may result, at least in part, from active habitat selection for high-organic sediments by settling larvae.

Assessing the role of bed sediments in the persistence of red mud pollution in a shallow lake (Kinghorn Loch, UK).

PubMed

Olszewska, Justyna P; Heal, Kate V; Winfield, Ian J; Eades, Lorna J; Spears, Bryan M

2017-10-15

Red mud is a by-product of alumina production. Little is known about the long-term fate of red mud constituents in fresh waters or of the processes regulating recovery of fresh waters following pollution control. In 1983, red mud leachate was diverted away from Kinghorn Loch, UK, after many years of polluting this shallow and monomictic lake. We hypothesised that the redox-sensitive constituents of red mud leachate, phosphorus (P), arsenic (As) and vanadium (V), would persist in the Kinghorn Loch for many years following pollution control as a result of cycling between the lake bed sediment and the overlying water column. To test this hypothesis, we conducted a 12-month field campaign in Kinghorn Loch between May 2012 and April 2013 to quantify the seasonal cycling of P, As, and V in relation to environmental conditions (e.g., dissolved oxygen (DO) concentration, pH, redox chemistry and temperature) in the lake surface and bottom waters. To confirm the mechanisms for P, As and V release, a sediment core incubation experiment was conducted using lake sediment sampled in July 2012, in which DO concentrations were manipulated to create either oxic or anoxic conditions similar to the bed conditions found in the lake. The effects on P, As, and V concentrations and species in the water column were measured daily over an eight-day incubation period. Phosphate (PO 4 -P) and dissolved As concentrations were significantly higher in the bottom waters (75.9 ± 30.2 μg L -1 and 23.5 ± 1.83 μg L -1 , respectively) than in the surface waters (12.9 ± 1.50 μg L -1 and 14.1 ± 2.20 μg L -1 , respectively) in Kinghorn Loch. Sediment release of As and P under anoxic conditions was confirmed by the incubation experiment and by the significant negative correlations between DO and P and As concentrations in the bottom waters of the lake. In contrast, the highest dissolved V concentrations occurred in the bottom waters of Kinghorn Loch under oxic conditions (15.0 ± 3.35 μg L -1 ), with the release from the bed sediment apparently being controlled by a combination of competitive ion concentrations, pH and redox conditions. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Remote sensing estimation of colored dissolved organic matter (CDOM) in optically shallow waters

NASA Astrophysics Data System (ADS)

Li, Jiwei; Yu, Qian; Tian, Yong Q.; Becker, Brian L.

2017-06-01

It is not well understood how bottom reflectance of optically shallow waters affects the algorithm performance of colored dissolved organic matters (CDOM) retrieval. This study proposes a new algorithm that considers bottom reflectance in estimating CDOM absorption from optically shallow inland or coastal waters. The field sampling was conducted during four research cruises within the Saginaw River, Kawkawlin River and Saginaw Bay of Lake Huron. A stratified field sampling campaign collected water samples, determined the depth at each sampling location and measured optical properties. The sampled CDOM absorption at 440 nm broadly ranged from 0.12 to 8.46 m-1. Field sample analysis revealed that bottom reflectance does significantly change water apparent optical properties. We developed a CDOM retrieval algorithm (Shallow water Bio-Optical Properties algorithm, SBOP) that effectively reduces uncertainty by considering bottom reflectance in shallow waters. By incorporating the bottom contribution in upwelling radiances, the SBOP algorithm was able to explain 74% of the variance of CDOM values (RMSE = 0.22 and R2 = 0.74). The bottom effect index (BEI) was introduced to efficiently separate optically shallow and optically deep waters. Based on the BEI, an adaptive approach was proposed that references the amount of bottom effect in order to identify the most suitable algorithm (optically shallow water algorithm [SBOP] or optically deep water algorithm [QAA-CDOM]) to improve CDOM estimation (RMSE = 0.22 and R2 = 0.81). Our results potentially help to advance the capability of remote sensing in monitoring carbon pools at the land-water interface.

Preliminary study of sources and processes of enrichment of manganese in water from University of Rhode Island supply wells

USGS Publications Warehouse

Silvey, William Dudley; Johnston, Herbert E.

1977-01-01

Concentrations of dissolved manganese have increased from 0.0 to as much as 3.3 mg/liter over a period of years in closely spaced University of Rhode Island supply wells. The wells tap stratified glacial deposits and derive part of their water from infiltration from a nearby river-pond system. The principal sources of the manganese seem to be coatings of oxides and other forms of manganese on granular aquifer materials and organic-rich sediments on the bottom of the pond and river. Chemical analyses of water from an observation well screened from 3 to 5 feet below the pond bottom indicate that infiltration of water through organic-rich sediments on the pond bottom is the likely cause of manganese enrichment in the well supplies. After passing through the organic layer, the water contains concentrations of manganese as high as 1.2 mg/liter. Manganese in water in concentrations that do not cause unpleasant taste is not regarded to be toxicologically significant. However, concentrations in excess of a few tenths of a milligram per liter are undesirable in public supplies and in many industrial supplies. Brown and others (21970) note that waters containing manganese in concentrations less than 0.1 mg/liter seldom prove troublesome, but that those containing more than 0.5 mg/liter may form objectionable deposits on cooked food, laundry, and plumbing fixtures. The U.S. Public health Service (1962) recommends that the concentrations of manganese in drinking and culinary water not exceed 0.05 mg/liter. (Woodard-USGS)

Analytical and numerical solution for wave reflection from a porous wave absorber

NASA Astrophysics Data System (ADS)

Magdalena, Ikha; Roque, Marian P.

2018-03-01

In this paper, wave reflection from a porous wave absorber is investigated theoretically and numerically. The equations that we used are based on shallow water type model. Modification of motion inside the absorber is by including linearized friction term in momentum equation and introducing a filtered velocity. Here, an analytical solution for wave reflection coefficient from a porous wave absorber over a flat bottom is derived. Numerically, we solve the equations using the finite volume method on a staggered grid. To validate our numerical model, comparison of the numerical reflection coefficient is made against the analytical solution. Further, we implement our numerical scheme to study the evolution of surface waves pass through a porous absorber over varied bottom topography.

Soil moisture transport in arid site vadose zones. [Evaluation of Hanford as national site for radioactive waste storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brownell, L.E.; Backer, J.G.; Isaacson, R.E.

1975-07-01

Data are presented from measurements of soil moisture at the Hanford Reservation. Possible mechanisms for moisture transport in arid and semi-arid climates were studied. Measurements for the lysimeter experiment and the thermocouple psychrometer experiment were continued with a new series of measurements using closely spaced sensors installed to a depth of 1.52 meters. During the 1973-1974 water year the percolation envelope of higher moisture content penetrated to a depth of four meters in the closed-bottom lysimeter and then was eliminated by upward transport of water in late summer. Precipitation during the 1973-1974 water year percolated to a depth of aboutmore » six meters in the open-bottom lysimeter and remains as a residual perched envelope. The increase over normal percolation was due in part to a residual envelope of higher moisture content from the previous water year. Results obtained indicate the advantages of Hanford as a site for a national repository for radioactive waste. (CH)« less

The results of initial analysis of OSTA-1/Ocean Color Experiment (OCE) imagery

NASA Technical Reports Server (NTRS)

Kim, H. H.; Hart, W. D.

1982-01-01

Ocean view images from the Ocean Color Experiment (OCE) were produced at three widely separated locations on the Earth. Digital computer enhancement and band ratioing techniques were applied to radiometrically corrected OCE spectral data to emphasize patterns of chlorophyll distribution and, in one shallow, clear water case, bottom topography. The chlorophyll pattern in the Yellow Sea between China and Korea was evident in a scene produced from Shuttle Orbit 24. The effects of the discharge from the Yangtze and other rivers were also observed. Two scenes from orbits 30 and 32 revealed the movement of patches of plankton in the Gulf of Cadiz. Geometrical corrections to these images permitted the existing ocean current velocities in the vicinity to be deduced. The variability in water depth over the Grand Bahama Bank was estimated by using the blue-green OCE channel. The very clear water conditions in the area caused bottom reflected sunlight to produce a sensor signal which was related inversely to the depth of the water.

Enrichment of free-living amoebae in biofilms developed at upper water levels in drinking water storage towers: An inter- and intra-seasonal study.

PubMed

Taravaud, Alexandre; Ali, Myriam; Lafosse, Bernard; Nicolas, Valérie; Féliers, Cédric; Thibert, Sylvie; Lévi, Yves; Loiseau, Philippe M; Pomel, Sébastien

2018-08-15

Free-living amoebae (FLA) are ubiquitous organisms present in various natural and artificial environments, such as drinking water storage towers (DWST). Some FLA, such as Acanthamoeba sp., Naegleria fowleri, and Balamuthia mandrillaris, can cause severe infections at ocular or cerebral level in addition to being potential reservoirs of other pathogens. In this work, the abundance and diversity of FLA was evaluated in two sampling campaigns: one performed over five seasons in three DWST at three different levels (surface, middle and bottom) in water and biofilm using microscopy and PCR, and one based on the kinetics analysis in phase contrast and confocal microscopy of biofilm samples collected every two weeks during a 3-month period at the surface and at the bottom of a DWST. In the seasonal study, the FLA were detected in each DWST water in densities of ~20 to 25amoebaeL -1 . A seasonal variation of amoeba distribution was observed in water samples, with maximal densities in summer at ~30amoebaeL -1 and minimal densities in winter at ~16amoebaeL -1 . The FLA belonging to the genus Acanthamoeba were detected in two spring sampling campaigns, suggesting a possible seasonal appearance of this potentially pathogenic amoeba. Interestingly, a 1 log increase of amoebae density was observed in biofilm samples collected at the surface of all DWST compared to the middle and the bottom where FLA were at 0.1-0.2amoebae/cm 2 . In the kinetics study, an increase of amoebae density, total cell density, and biofilm thickness was observed as a function of time at the surface of the DWST, but not at the bottom. To our knowledge, this study describes for the first time a marked higher FLA density in biofilms collected at upper water levels in DWST, constituting a potential source of pathogenic micro-organisms. Copyright © 2018 Elsevier B.V. All rights reserved.

Under-ice melt ponds in the Arctic

NASA Astrophysics Data System (ADS)

Smith, Naomi; Flocco, Daniela; Feltham, Daniel

2017-04-01

In the summer months, melt water from the surface of the Arctic sea ice can percolate down through the ice and flow out of its base. This water is relatively warm and fresh compared to the ocean water beneath it, and so it floats between the ice and the oceanic mixed layer, forming pools of melt water called under-ice melt ponds. Double diffusion can lead to the formation of a sheet of ice, which is called a false bottom, at the interface between the fresh water and the ocean. These false bottoms isolate under-ice melt ponds from the ocean below, trapping the fresh water against the sea ice. These ponds and false bottoms have been estimated to cover between 5 and 40% of the base of the sea ice. [Notz et al. Journal of Geophysical Research 2003] We have developed a one-dimensional thermodynamic model of sea ice underlain by an under-ice melt pond and false bottom. Not only has this allowed us to simulate the evolution of under-ice melt ponds over time, identifying an alternative outcome than previously observed in the field, but sensitivity studies have helped us to estimate the impact that these pools of fresh water have on the mass-balance sea ice. We have also found evidence of a possible positive feedback cycle whereby increasingly less ice growth is seen due to the presence of under-ice melt ponds as the Arctic warms. Since the rate of basal ablation is affected by these phenomena, their presence alters the salt and freshwater fluxes from the sea ice into the ocean. We have coupled our under-ice melt pond model to a simple model of the oceanic mixed layer to determine how this affects mixed layer properties such as temperature, salinity, and depth. In turn, this changes the oceanic forcing reaching the sea ice.

Seasonal seafloor oxygen dynamics on the Romanian Black Sea Shelf

NASA Astrophysics Data System (ADS)

Friedrich, Jana; Balan, Sorin; van Beusekom, Justus E.; Naderipour, Celine; Secrieru, Dan

2017-04-01

The Black Sea suffers from the combined effects of anthropogenic eutrophication, overfishing and climate forcing. As a result, its broad and shallow western shelf in particular has a history of ecosystem collapse during the 1970s to the mid-1990s, which followed a slow recovery since the late 1990s due to reduction in anthropogenic pressures. Because of eutrophication, increased oxygen consumption caused recurrent widespread seasonal seafloor hypoxia in a system that is already naturally prone to decrease in bottom water oxygen during summer. On the shelf, reduced bottom water ventilation is a strong natural driver for seafloor hypoxia, due to strong seasonal thermohaline stratification as a result of freshwater inflow from the large rivers Danube, Dniester and Dniepro. To understand the present seasonal dynamics of seafloor oxygen on the Romanian shelf, a seafloor mooring was deployed in 2010 and 2016 during summer and autumn, for three and six months, respectively. The mooring, consisting of an Aanderaa SEAGUARD sensor package attached to an acoustic release, was deployed in 30 m water depth in the Portita region - north of Constanta and south of the Danube River Mouths. The in-situ time series of seafloor oxygen, temperature, turbidity, salinity, and current velocities and directions, combined with CTD profiles, benthic oxygen consumption rates based on ex-situ incubations of sediment cores, and pelagic oxygen respiration rates provide a set of information that allows biological and hydrophysical controls on seafloor oxygen to be identified. We observed the built-up of the thermohaline stratification during late spring and early summer, accompanied by steady decrease in bottom water oxygen. Superimposed settling of particles to the seafloor eventually led to the formation of seafloor hypoxia in late summer. Anticyclonic currents resemble diurnal tidal cycles, albeit low in magnitude. The effects of a strong rainstorm and a Danube flood event in late September were visible in a short-term increase in bottom water oxygen. The autumn storm events over the Black Sea led to seafloor ventilation and stepwise increase of bottom water oxygen on the shelf, which continues during the stormy winter season.

Ridge Flank Flux as a Potential Source for the North Pacific Silica Plume

NASA Astrophysics Data System (ADS)

Johnson, H. P.; Hautala, S. L.; Bjorklund, T. A.

2005-12-01

The North Pacific silica plume is a global scale anomaly, extending from the North American continental margin to west of the Hawaii-Emperor seamount chain. Inventory of the plume at depths between 2000 and 3000 meters indicates that it contains 164 Teramols of dissolved silica, and is maintained by a horizontal flux of approximately 1.5 Tmols/year from the Eastern Pacific. The source region of this silica plume has been previously reported to be Cascadia Basin in the NE Pacific. However, simple box models based both on new hydrostations and compilations of archive data indicate that only a third of the dissolved silica that enters the larger North Pacific plume originates locally within the Cascadia/Gorda Basin. As it encounters the North American continental margin, the eastward-flowing deep Pacific bottom water is forced into `a U-turn' by seafloor topography. A portion of the bottom water is elevated from 4000 to 2300 meter depths by the high geothermal heat flow during rapid passage through Cascadia/Gorda Basin, and subsequently flows westward as the North Pacific mid-water plume. The plume water also absorbs an estimated 0.47 Tmol/year of locally derived silica during its passage adjacent to the continental margin. However, the Pacific bottom water is already relatively enriched in dissolved silica when it passes the Gorda Ridge/Mendocino junction, and the remaining 1 Tmol/year of silica must be acquired during near-bottom transit from the Western Pacific, over the portion of the easternmost Pacific plate where basement is younger than 65 Ma. Global compilations based on heat flow data argue that the upper crustal section of the young, eastern Pacific plate is an enormous aquifer, with active hydrothermal circulation and presumably diffuse venting into the bottom water. The suggestion that the large-scale flux of silica-rich hydrothermal fluid from the young eastern portion of the Pacific plate contributes to the North Pacific silica plume is a consequence of that interpretation, but is only a plausible and still untested hypothesis. If correct, however, it implies that the ridge flanks of the eastern Pacific Ocean are a global-scale source of a critically important nutrient.

Role of mariculture in the loading and speciation of mercury at the coast of the East China Sea.

PubMed

Liang, Peng; Gao, Xuefei; You, Qiongzhi; Zhang, Jin; Cao, Yucheng; Zhang, Chan; Wong, Ming-Hung; Wu, Sheng-Chun

2016-11-01

The effects of mariculture on mercury (Hg) contamination and speciation in water, sediment and cultured fish in a typical mariculture zone located in Xiangshan bay, Zhejiang province, east China, were studied. Water, sediment and fish samples were collected from mariculture sites (MS) and from corresponding reference sites (RS) 2500 m away from the MS. The THg concentration in overlying water in Xiangshan bay reached as high as 16.6 ± 19.5 ng L -1 , indicating that anthropogenic sources in this bay may contribution on Hg contamination in overlying water. Mariculture activities resulted in an increase in THg concentration in water from surface and bottom layers, which may be attributed to the discharge of domestic sewage and the accumulation of unconsumed fish feed and fish excreta in the benthic environment. Methylmercury (MeHg) concentrations in the bottom layer of overlying water and top surface layer of porewater underneath MS were higher than at RS, implying that mariculture activities promote Hg methylation in the interface between sediments and water. In addition, the concentrations of MeHg in sediment and porewater were significantly higher in summer than winter. It was observed that THg and MeHg contents in the muscle of blackhead seabream (Acanthopagrus schlegelii) (fed by the trash fish) were significantly higher (p < 0.001) than those in red snapper (Lutjanus campechanus) or perch (Perca fluviatilis) (fed by pellet fish feed). The THg and MeHg concentrations in the fish meat were closely related to the feeding mode, which indicate that fish feed rather than environmental media is the major pathway for Hg accumulation in fish muscle. Copyright © 2016 Elsevier Ltd. All rights reserved.

Design and use of a sparged platform for energy flux measurements over lakes

NASA Astrophysics Data System (ADS)

Gijsbers, S.; Wenker, K.; van Emmerik, T.; de Jong, S.; Annor, F.; Van De Giesen, N.

2012-12-01

Energy flux measurements over lakes or reservoirs demand relatively stable platforms. Platforms can not be stabilized by fixing them on the bottom of the lake when the water body is too deep or when water levels show significant fluctuations. We present the design and first operational results of a sparged platform. The structure consists of a long PVC pipe, the sparge, which is closed at the bottom. On the PVC pipe rests an aluminum frame platform that carries instrumentation and solar power panel. In turn, the platform rests partially on a large inflated tire. At the bottom of the PVC pipe, lead weights and batteries were placed to ensure a very low point of gravity to minimize wave impact on the platform movement. The tire ensures a large second moment of the water plane. The overall volume of displacement is small in this sparged design. The combination of large second momentum of the water plane and small displacement ensure a high placement of the metacenter. The distance between the point of gravity and the metacenter is relatively long and the weight is large due to the weights and batteries. This ensures that the eigenfrequency of the platform is very low. The instrumentation load consisted of a WindMaster Pro (sonic anemometer for 3D wind speed and air temperature to perform eddy covariance measurements of sensible heat flux), a NR Lite (net radiometer), and air temperature and relative humidity sensors. The platform had a wind vane and the sparge could turn freely around its anchor cable to ensure that the anemometer always faced upwind. A compass in the logger completed this setup. The stability was measured with an accelerometer. In addition to the design and its stability, some first energy flux results will be presented.

Life cycle assessment of disposal of residues from municipal solid waste incineration: recycling of bottom ash in road construction or landfilling in Denmark evaluated in the ROAD-RES model.

PubMed

Birgisdóttir, H; Bhander, G; Hauschild, M Z; Christensen, T H

2007-01-01

Two disposal methods for MSWI bottom ash were assessed in a new life cycle assessment (LCA) model for road construction and disposal of residues. The two scenarios evaluated in the model were: (i) landfilling of bottom ash in a coastal landfill in Denmark and (ii) recycling of bottom ash as subbase layer in an asphalted secondary road. The LCA included resource and energy consumption, and emissions associated with upgrading of bottom ash, transport, landfilling processes, incorporation of bottom ash in road, substitution of natural gravel as road construction material and leaching of heavy metals and salts from bottom ash in road as well as in landfill. Environmental impacts associated with emissions to air, fresh surface water, marine surface water, groundwater and soil were aggregated into 12 environmental impact categories: Global Warming, Photochemical Ozone Formation, Nutrient Enrichment, Acidification, Stratospheric Ozone Depletion, Human Toxicity via air/water/soil, Ecotoxicity in water/soil, and a new impact category, Stored Ecotoxicity to water/soil that accounts for the presence of heavy metals and very persistent organic compounds that in the long-term might leach. Leaching of heavy metals and salts from bottom ash was estimated from a series of laboratory leaching tests. For both scenarios, Ecotoxicity(water) was, when evaluated for the first 100 yr, the most important among the twelve impact categories involved in the assessment. Human Toxicity(soil) was also important, especially for the Road scenario. When the long-term leaching of heavy metals from bottom ash was evaluated, based on the total content of heavy metals in bottom ash, all impact categories became negligible compared to the potential Stored Ecotoxicity, which was two orders of magnitudes greater than Ecotoxicity(water). Copper was the constituent that gave the strongest contributions to the ecotoxicities. The most important resources consumed were clay as liner in landfill and the groundwater resource which was potentially spoiled due to leaching of salts from bottom ash in road. The difference in environmental impacts between landfilling and utilization of bottom ash in road was marginal when these alternatives were assessed in a life cycle perspective.

Quality of water and chemistry of bottom sediment in the Rillito Creek basin, Tucson, Arizona, 1986-92

USGS Publications Warehouse

Tadayon, Saeid; Smith, C.F.

1994-01-01

Data were collected on physical properties and chemistry of 4 surface water, l4 ground water, and 4 bottom sediment sites in the Rillito Creek basin where artificial recharge of surface runoff is being considered. Concentrations of suspended sediment in streams generally increased with increases in streamflow and were higher during the summer. The surface water is a calcium and bicarbonate type, and the ground water is calcium sodium and bicarbonate type. Total trace ek=nents in surface water that exceeded the U.S. Environmental Protection Agency primary maximum contaminant levels for drinking-water standards were barium, beryllium, cadmium, chromium, lead, mercury and nickel. Most unfiltered samples for suspended gross alpha as uranium, and unadjusted gross alpha plus gross beta in surface water exceeded the U.S. Environmental Protection Agency and the State of Arizona drinking-water standards. Comparisons of trace- element concentrations in bottom sediment with those in soils of the western conterminous United States generally indicate similar concentrations for most of the trace elements, with the exceptions of scandium and tin. The maximum concentration of total nitrite plus nitrate as nitrogen in three ground- samples and total lead in one ground-water sample exceeded U.S. Environmental Protection Agency primary maximum contaminant levels for drinking- water standards, respectively. Seven organochlorine pesticides were detected in surface-water samples and nine in bottom-sediment samples. Three priority pollutants were detected in surface water, two were detected in ground water, and eleven were detected in bottom sediment. Low concentrations of oil and grease were detected in surface-water and bottom- sediment samples.

Numerical model for a watering plan to wash out organic matter from the municipal solid waste incinerator bottom ash layer in closed system disposal facilities.

PubMed

Ishii, Kazuei; Furuichi, Toru; Tanikawa, Noboru

2009-02-01

Bottom ash from municipal solid waste incineration (MSWI) is a main type of waste that is landfilled in Japan. The long-term elution of organic matter from the MSWI bottom ash layers is a concern because maintenance and operational costs of leachate treatment facilities are high. In closed system disposal facilities (CSDFs), which have a roof to prevent rainfall from infiltrating into the waste layers, water must be supplied artificially and its quantity can be controlled. However, the quantity of water needed and how to apply it (the intensity, period and frequency) have not been clearly defined. In order to discuss an effective watering plan, this study proposes a new washout model to clarify a fundamental mechanism of total organic carbon (TOC) elution behavior from MSWI bottom ash layers. The washout model considers three phases: solid, immobile water and mobile water. The parameters, including two mass transfer coefficients of the solid-immobile water phases and immobile-mobile water phases, were determined by one-dimensional column experiments for about 2 years. The intensity, period and frequency of watering and other factors were discussed based on a numerical analysis using the above parameters. As a result, our washout model explained adequately the elution behavior of TOC from the MSWI bottom ash layer before carbonation occurred (pH approximately 8.3). The determined parameters and numerical analysis suggested that there is a possibility that the minimum amount of water needed for washing out TOC per unit weight of MSWI bottom ash layer could be determined, which depends on the two mass transfer coefficients and the depth of the MSWI bottom ash layer. Knowledge about the fundamental mechanism of the elution behavior of TOC from the MSWI bottom ash layer before carbonation occurs, clarified by this study, will help an effective watering plan in CSDFs.

The geological setting of Santa Monica and San Pedro Basins, California Continental Borderland

NASA Astrophysics Data System (ADS)

Gorsline, D. S.

The California Continental Borderland's present configuration dates from about 4 to 5 × 10 6 years before present (BP) and is the most recent of several configuration of the southern California margin that have evolved after the North America plate over-rode the East Pacific Rise about 30 × 10 6 years ago. The present morphology is a series of two to three northwest-southeast trending rows of depressions separated by banks and insular ridges. Two inner basins, Santa Monica and San Pedro, have been the site for the California Basin Study (CaBs), funded by the US Department of Energy. The Santa Monica and San Pedro Basins contain post-Miocene sediment thicknesses of about 2.5 and 1.5 km respectively. During the Holocene (past 10,000 years) about 10-12m have accumulated. The sediment entered the basin by one or a combination of processes including particle infall (mainly as bioaggregates) from surface waters, from nepheloid plumes (surface, mid-depth and near-bottom), from turbidity currents, mass movements, and to a very minor degree direct precipitation. In Santa Monica Basin, during the last century, particle infall nepheloid plume transport have been the most common processes. The former process has been dominant in thecentral basin at water depths from 900-945m, where characteristic silt-clay is found with a typical mean particle diameter of about 0.0006mm ( φ standard deviation = 2; φ skewness near zero). Kurtosis is typically 2 (platykurtic); these values indicate broad, near-log normal particle size distributions. The calcium carbonate content averages about 10% and organic carbon about 4%. Surficial sediment bulk densities are 1.1-1.2 and accumulation rates range from 16-30mg cm -2Yr 1 in this central fine deposit. Bottom water oxygen contents are at or below 0.1 ml 1 -1 so that bioturbation is inhibited, thus preserving the primary sedimentary stratification. There appear to be annual varves, but the laminae couplets are not simple wet-dry season pairs. Their formation is related to longer period climatic events (El Niño cycle of 3 to 4 years is dominant), and is also affected by aperiodic bottom water flushing events. The “anoxic” zone of bottom water has expanded over the past 300 to 350 years from a samll area in the northeastern basin floor (ca 120km 2 at 300 years BP), and now covers most of the basin floor below depths of about 850m (1290km 2). This expansion may have been primarily relaed to ocean circulation rate changes following the Little Ice Age, but is also likely to have been strongly affected by subsequent major changes in the natural drainages post-European colonization. The bottom water oxygen contents must also reflect the introduction of oxidizable pollutants, coincident with the shift to agricultural (Mission era) and then to urban use (late 19th century to present) of the adjacent mainland. Such localized effects are also suggested by the contrasting very large increases in the area of low oxygen bottom water in Santa Monica Basin relative to the minimal changes in the area of anoxia in Santa Barbara Basin over the same period and the lack of such zone in San Pedro Basin. In the San Pedro Basin the bottom waters have remained dysaerobic so its sediments are bioturbated and preserve little or no evidence of primary stratification. Dumping of oil drilling muds and cuttings during the couple of decades prior to 1970 has left a surficial deposit ranging from 1 to 15cm in thickness, forming a bull's eye isopach pattern as seen in radiographs. Bottom water oxygen content is usually >0.2ml O 21 -1. Bottom infauna and epifauna are sparse. Central basin floor sediments (water depths>800m) of San Pedro Basin have textural characteristics similar to those of Santa Monica Basin with distal basin floor surficial sediments being deposited primarily by particle infall and nepheloid flow at the present time. (Mean diameters ≈0.006mm, φ standard deviation ≈ 2, φ skewness ≈ 0 and kurtosis ≈ 2 (platykurtic). Calcium carbonate content averages 8-10% and organic carbon is about 4%. An estimate of the contemporary sedimentation rate was determined for a single box core of 25-29mg cm -2 yr 1 from the central basin near the present distributary margin; it cannot be considered necessarily to be representative. Mixing is indicated by the data. An important climatic factor is the alternation of multi-year wet and dry periods. The California Basin Study was conducted during an extended dry period of low river discharge. This undoubtedly will have affected the conclusions of the study related to sediment-water interactions and pollutant transport by suspended clays.

Particle Mass in Deep-Water Benthic Nepheloid Layers: a Global Synthesis

NASA Astrophysics Data System (ADS)

Mishonov, A. V.; Gardner, W. D.; Richardson, M. J.

2016-12-01

The mass of particles in benthic nepheloid layers in the deep ocean is mapped using profiles of beam attenuation coefficient obtained with transmissometers interfaced with CTDs during WOCE, SAVE, JGOFS, CLIVAR-Repeat Hydrography, and other programs during the last four decades using data from over 8000 profiles from >70 cruises. We map the maximum concentration of particle mass near the seafloor and integrate the particle mass throughout the benthic nepheloid layer. In the Atlantic Ocean particle mass is greater in areas where eddy kinetic energy is high in overlying waters. Areas of high bottom particle concentrations and integrated benthic nepheloid layer particle loads include the western North Atlantic beneath the Gulf Stream meanders and eddies, Argentine Basin, parts of the Southern Ocean and areas around South Africa. Particle concentrations are low in most of the Pacific and tropical and subtropical Atlantic away from margins. This synthesis is useful for GEOTRACES and other global programs where knowing particle distribution is critical for understanding trace metal absorption, sediment-water exchange and near-bottom processes. Additionally, our synthesis provides baseline data to identify where mining of metal-rich nodules and metal sulfides on the seafloor may impact the benthic environment.

Inter-decadal changes in the intensity of the Oxygen Minimum Zone off Concepción, Chile (~ 36° S) over the last century

NASA Astrophysics Data System (ADS)

Srain, B.; Pantoja, S.; Sepúlveda, J.; Lange, C. B.; Muñoz, P.; Summons, R. E.; McKay, J.; Salamanca, M.

2015-04-01

We reconstructed oxygenation changes in the Oxygen Minimum Zone of the upwelling ecosystem off Concepción (36° S), Chile, using inorganic and organic proxies in a sediment core covering the last ca. 110 years of sedimentation in this area. Authigenic enrichments of Mo, U and Cd were observed between ca. 1935-1971 CE indicating a prolonged period of more reduced conditions in bottom waters and surface sediments. Significant positive correlations (p < 0.05; Spearman) between redox sensitive metals, algal sterols, biomarkers of anaerobic microorganisms, and archaeal glycerol dialkyl glycerol tetraether indicated a coupling among bottom water oxygen depletion, and increased primary and export production, suggesting that the period with low O2 of ca. 35 years, follows low frequency inter-decadal variation of the Pacific Decadal Oscillation, which may have resulted in O2 depletion over the entire continental shelf off Concepción. Taken together with the concurrent increase in sedimentary molecular indicators of anaerobic microbes allow us to suggest that the prokaryote community has been influenced by changes in oxygenation of the water column.

Mechanisms of wave‐driven water level variability on reef‐fringed coastlines

USGS Publications Warehouse

Buckley, Mark L.; Lowe, Ryan J.; Hansen, Jeff E; van Dongeren, Ap R.; Storlazzi, Curt

2018-01-01

Wave‐driven water level variability (and runup at the shoreline) is a significant cause of coastal flooding induced by storms. Wave runup is challenging to predict, particularly along tropical coral reef‐fringed coastlines due to the steep bathymetric profiles and large bottom roughness generated by reef organisms, which can violate assumptions in conventional models applied to open sandy coastlines. To investigate the mechanisms of wave‐driven water level variability on a reef‐fringed coastline, we performed a set of laboratory flume experiments on an along‐shore uniform bathymetric profile with and without bottom roughness. Wave setup and waves at frequencies lower than the incident sea‐swell forcing (infragravity waves) were found to be the dominant components of runup. These infragravity waves were positively correlated with offshore wave groups, signifying they were generated in the surf zone by the oscillation of the breakpoint. On the reef flat and at the shoreline, the low‐frequency waves formed a standing wave pattern with energy concentrated at the natural frequencies of the reef flat, indicating resonant amplification. Roughness elements used in the flume to mimic large reef bottom roughness reduced low frequency motions on the reef flat and reduced wave run up by 30% on average, compared to the runs over a smooth bed. These results provide insight into sea‐swell and infragravity wave transformation and wave setup dynamics on steep‐sloped coastlines, and the effect that future losses of reef bottom roughness may have on coastal flooding along reef‐fringed coasts.

Sense Things in the Big Deep Water Bring the Big Deep Water to Computers so People can understand the Deep Water all the Time without getting wet

NASA Astrophysics Data System (ADS)

Pelz, M.; Heesemann, M.; Scherwath, M.; Owens, D.; Hoeberechts, M.; Moran, K.

2015-12-01

Senses help us learn stuff about the world. We put sense things in, over, and under the water to help people understand water, ice, rocks, life and changes over time out there in the big water. Sense things are like our eyes and ears. We can use them to look up and down, right and left all of the time. We can also use them on top of or near the water to see wind and waves. As the water gets deep, we can use our sense things to see many a layer of different water that make up the big water. On the big water we watch ice grow and then go away again. We think our sense things will help us know if this is different from normal, because it could be bad for people soon if it is not normal. Our sense things let us hear big water animals talking low (but sometimes high). We can also see animals that live at the bottom of the big water and we take lots of pictures of them. Lots of the animals we see are soft and small or hard and small, but sometimes the really big ones are seen too. We also use our sense things on the bottom and sometimes feel the ground shaking. Sometimes, we get little pockets of bad smelling air going up, too. In other areas of the bottom, we feel hot hot water coming out of the rock making new rocks and we watch some animals even make houses and food out of the hot hot water that turns to rock as it cools. To take care of the sense things we use and control water cars and smaller water cars that can dive deep in the water away from the bigger water car. We like to put new things in the water and take things out of the water that need to be fixed at least once a year. Sense things are very cool because you can use the sense things with your computer too. We share everything for free on our computers, which your computer talks to and gets pictures and sounds for you. Sharing the facts from the sense things is the best part about having the sense things because we can get many new ideas about understanding the big water from anyone with a computer!

Effects of regional climate changes on the planktonic ecosystem and water environment in the frozen Notoro Lagoon, northern Japan.

PubMed

Katsuki, Kota; Seto, Koji; Noguchi, Takuro; Sonoda, Takeshi; Kim, JuYong

2012-10-01

Diatom fossils from core sediments and living diatoms from water samples of Notoro Lagoon in northern Japan were examined to evaluate natural climate effects on lagoon environmental changes. In 1974, the artificial inlet was excavated. Immediately after, the anoxic bottom water in Notoro Lagoon began to disappear due to an increasing water exchange rate. However, chemical oxygen demand (COD) in the bottom water of Notoro Lagoon gradually increased, with fluctuations, during the last 30 years. In addition, the dominant diatom assemblages in Notoro Lagoon shifted to ice-related and spring bloom taxa after the excavation. The dominant taxa of each year in the sediment core were also strongly related to the timing of lagoon ice melting. This is because the COD in Notoro Lagoon was affected by the deposited volume of blooming diatoms, which was controlled by the duration of ice cover and the timing of ice discharge to the Okhotsk Sea likely due to an air pressure pattern change over the northern North Pacific like the Pacific Decadal Oscillation (PDO). Copyright © 2012 Elsevier Ltd. All rights reserved.

Chemical characteristics of hadal waters in the Izu-Ogasawara Trench of the western Pacific Ocean.

PubMed

Gamo, Toshitaka; Shitashima, Kiminori

2018-01-01

Vertical profiles of potential temperature, salinity, and some chemical components were obtained at a trench station (29°05'N, 142°51'E; depth = 9768 m) in the Izu-Ogasawara (Bonin) Trench in 1984 and 1994 to characterize the hadal waters below ∼6000 m depth. We compared portions of both the 1984 and 1994 profiles with nearby data obtained between 1976 and 2013. Results demonstrated that the hadal waters had slightly higher potential temperature and nitrate and lower dissolved oxygen than waters at sill depths (∼6000 m) outside the trench, probably due to the effective accumulation of geothermal heat and active biological processes inside the trench. The silicate, iron, and manganese profiles in 1984 showed slight but significant increases below ∼6000 m depth, suggesting that these components may have been intermittently supplied from the trench bottom. Significant amounts of 222 Rn in excess over 226 Ra were detected in the hadal waters up to 2675 m from the bottom, reflecting laterally supplied 222 Rn from the trench walls.

A downslope propagating thermal front over the continental slope

NASA Astrophysics Data System (ADS)

van Haren, Hans; Hosegood, Phil J.

2017-04-01

In the ocean, internal frontal bores above sloping topography have many appearances, depending on the local density stratification, and on the angle and source of generation of the carrier wave. However, their common characteristics are a backward breaking wave, strong sediment resuspension, and relatively cool (denser) water moving more or less upslope underneath warm (less dense) water. In this paper, we present a rare example of a downslope moving front of cold water moving over near-bottom warm water. Large backscatter is observed in the downslope moving front's trailing edge, rather than the leading edge as is common in upslope moving fronts. Time series observations have been made during a fortnight in summer, using a 101 m long array of high-resolution temperature sensors moored with an acoustic Doppler current profiler at 396 m depth in near-homogeneous waters, near a small canyon in the continental slope off the Malin shelf (West-Scotland, UK). Occurring between fronts that propagate upslope with tidal periodicity, the rare downslope propagating one resembles a gravity current and includes strong convective turbulence coming from the interior rather than the more usual frictionally generated turbulence arising from interaction with the seabed. Its turbulence is 3-10 times larger than that of more common upslope propagating fronts. As the main turbulence is in the interior with a thin stratified layer close to the bottom, little sediment is resuspended by a downslope propagating front. The downslope propagating front is suggested to be generated by oblique propagation of internal (tidal) waves and flow over a nearby upstream promontory.

Rapid Changes in Water Properties on a Shallow Reef in the Chesapeake Bay due to a Wind Driven Internal Seiche

NASA Astrophysics Data System (ADS)

Kilbourne, B.

2016-12-01

The Chesapeake Bay Interpretive Buoy System has collected oceanographic and meteorological observations in Chesapeake Bay from 2007 to the present. The relatively long and well resolved time series of wind, current, and salinity data provided by this array creates an opportunity to better understand the many finescale circulation pathways in Chesapeake Bay. The mean vertical structure of Chesapeake Bay is approximated by a three layer system: a well-mixed surface boundary layer from 1 to 8 m depth, a stratified transition layer from 8 to 15 m depth, and a well-mixed bottom boundary layer from 15 m to the bottom (typically < 30 m). The conditions in the surface and bottom boundary layers can be strikingly different with the bottom layer being saltier, lower in pH, and lower in dissolved oxygen than the surface layer. The Gooses Reef station of this array is located on `Gooses Reef', a shallow bar just 10 m in depth, dividing the Choptank River basin from the main channel of the Chesapeake Bay. This shallow bar provides habitat for oysters, a keystone species in the Chesapeake Bay, and is both commercially and ecologically critical to the region. These shallow habitats are threatened when anoxic (< 0.5 mg l-1 O2) conditions exist in the upper 10 m of the water column. The Gooses Reef station is unique in the array due to the addition of a bottom mounted sensor package; data from August 2012 show rapid changes in the salinity (11 to 17 PSU), dissolved oxygen (6 to 0.05 mg l-1) , and pH (8.3 to 7.7) at the bottom. Investigations of wind and current data before these rapid changes show along channel wind stress oscillations near the M2 tidal frequency. Current profiles from the buoy ADCP show low-frequency along-channel baroclinic oscillations. Observed currents appear to be an internal seiche, forced by resonance between the along-channel wind and diurnal tide. At the Gooses Reef bar, this internal seiche forced the bottom boundary layer up and over the bar, causing the sudden shift in water properties. These observations highlight the strong physical controls on local water conditions in the Chesapeake Bay and similar estuaries.

Selenium and trace element mobility affected by periodic displacement of stratification in the Great Salt Lake, Utah

USGS Publications Warehouse

Beisner, K.; Naftz, D.L.; Johnson, W.P.; Diaz, X.

2009-01-01

The Great Salt Lake (GSL) is a unique ecosystem in which trace element activity cannot be characterized by standard geochemical parameters due to the high salinity. Movement of selenium and other trace elements present in the lake bed sediments of GSL may occur due to periodic stratification displacement events or lake bed exposure. The water column of GSL is complicated by the presence of a chemocline persistent over annual to decadal time scales. The water below the chemocline is referred to as the deep brine layer (DBL), has a high salinity (16.5 to 22.9%) and is anoxic. The upper brine layer (UBL) resides above the chemocline, has lower salinity (12.6 to 14.7%) and is oxic. Displacement of the DBL may involve trace element movement within the water column due to changes in redox potential. Evidence of stratification displacement in the water column has been observed at two fixed stations on the lake by monitoring vertical water temperature profiles with horizontal and vertical velocity profiles. Stratification displacement events occur over periods of 12 to 24 h and are associated with strong wind events that can produce seiches within the water column. In addition to displacement events, the DBL shrinks and expands in response to changes in the lake surface area over a period of months. Laboratory tests simulating the observed sediment re-suspension were conducted over daily, weekly and monthly time scales to understand the effect of placing anoxic bottom sediments in contact with oxic water, and the associated effect of trace element desorption and (or) dissolution. Results from the laboratory simulations indicate that a small percentage (1%) of selenium associated with anoxic bottom sediments is periodically solubilized into the UBL where it potentially can be incorporated into the biota utilizing the oxic part of GSL.

Sedimentation and occurrence and trends of selected nutrients, other chemical constituents, and cyanobacteria in bottom sediment, Clinton Lake, northeast Kansas, 1977-2009

USGS Publications Warehouse

Juracek, Kyle E.

2011-01-01

A combination of available bathymetric-survey information and bottom-sediment coring was used to investigate sedimentation and the occurrence of selected nutrients (total nitrogen and total phosphorus), organic and total carbon, 25 trace elements, cyanobacterial akinetes, and the radionuclide cesium-137 in the bottom sediment of Clinton Lake, northeast Kansas. The total estimated volume and mass of bottom sediment deposited from 1977 through 2009 in the conservation (multi-purpose) pool of the reservoir was 438 million cubic feet and 18 billion pounds, respectively. The estimated sediment volume occupied about 8 percent of the conservation-pool, water-storage capacity of the reservoir. Sedimentation in the conservation pool has occurred about 70 percent faster than originally projected at the time the reservoir was completed. Water-storage capacity in the conservation pool has been lost to sedimentation at a rate of about 0.25 percent annually. Mean annual net sediment deposition since 1977 in the conservation pool of the reservoir was estimated to be 563 million pounds per year. Mean annual net sediment yield from the Clinton Lake Basin was estimated to be 1.5 million pounds per square mile per year. Typically, the bottom sediment sampled in Clinton Lake was at least 99 percent silt and clay. The mean annual net loads of total nitrogen and total phosphorus deposited in the bottom sediment of Clinton Lake were estimated to be 1.29 million pounds per year and 556,000 pounds per year, respectively. The estimated mean annual net yields of total nitrogen and total phosphorus from the Clinton Lake Basin were 3,510 pounds per square mile per year and 1,510 pounds per square mile per year, respectively. Throughout the history of Clinton Lake, total nitrogen concentrations in the deposited sediment generally were uniform and indicated consistent inputs to the reservoir over time. Likewise, total phosphorus concentrations in the deposited sediment generally were uniform. Although, for two of three coring sites, a possible positive trend in phosphorus deposition was indicated. The Wakarusa River possibly was a larger contributor of nitrogen and phosphorus to Clinton Lake than was Rock Creek. As a principal limiting factor for primary production in most freshwater environments, phosphorus is of particular importance because increased inputs can contribute to accelerated reservoir eutrophication and the production of algal toxins and taste-and-odor compounds. Trace-element concentrations in the bottom sediment of Clinton Lake generally were uniform over time. As is typical for eastern Kansas reservoirs, arsenic, chromium, and nickel concentrations typically exceeded the threshold-effects guidelines, which represent the concentrations above which toxic biological effects occasionally occur. Zinc concentrations frequently exceeded the threshold-effects guideline. Trace-element concentrations did not exceed the probable-effects guidelines (available for eight trace elements), which represent the concentrations above which toxic biological effects usually or frequently occur. Cyanobacterial akinetes (cyanobacteria resting stage) in the bottom sediment of Clinton Lake, combined with historical water-quality data on chlorophyll-a and total phosphorus concentrations, indicated that the reservoir likely has been eutrophic throughout most of its history. A statistically significant increase in cyanobacterial akinetes in the bottom sediment indicated that Clinton Lake may have become more eutrophic over the life of the reservoir. The increase in cyanobacterial akinetes may, in part, be related to a possible increase in total phosphorus concentrations.

Benthic nitrogen turnover processes in coastal sediments at the Danube Delta

NASA Astrophysics Data System (ADS)

Bratek, Alexander; Dähnke, Kirstin; Neumann, Andreas; Möbius, Jürgen; Graff, Florian

2017-04-01

The Black Sea Shelf has been exposed to strong anthropogenic pressures from intense fisheries and high nutrient inputs and eutrophication over the past decades. In the light of decreasing riverine nutrient loads and improving nutrient status in the water column, nutrient regeneration in sediments and biological N-turnover in the Danube Delta Front have an important effect on nutrient loads in the shelf region. In May 2016 we determined pore water nutrient profiles in the Danube River Delta-Black Sea transition zone, aiming to assess N-regeneration and elimination based on nutrient profiles and stable N- isotope changes (nitrate and ammonium) in surface water masses and in pore water. We aimed to investigate the magnitude and isotope values of sedimentary NH4+ and NO3- and their impact on the current N-budget in Black Sea Shelf water. Based on changes in the stable isotope ratios of NO3- and NH4+, we aimed to differentiate diffusion and active processing of ammonium as well as nitrate sources and sinks in bottom water. First results show that the concentration of NH4+ in pore water increases with depth, reaching up to 1500 µM in deeper sediment layers. We find indications for high fluxes of ammonium to the overlying water, while stable isotope profiles of ammonium suggest that further processing, apart from mere diffusion, acts on the pore water ammonium pool. Nitrate concentration and stable isotope profiles show rapid consumption in deeper anoxic sediment layers, but also suggest that nitrate regeneration in bottom water increases the dissolved nitrate pool. Overall, the isotope and concentration data of pore water ammonium clearly mirror a combination of turnover processes and diffusion.

Quality of water and chemistry of bottom sediment in the Rillito Creek basin, Tucson, Arizona, 1992-93

USGS Publications Warehouse

Tadayon, Saeid

1995-01-01

Physical and chemical data were collected from four surface-water sites, six ground-water sites, and two bottom-sediment sites during 1992-93. Specific conductance, hardness, alkalinity, and dissolved- solids concentrations generally were higher in ground water than in surface water. The median concentrations of dissolved major ions, with the exception of potassium, were higher in ground water than in surface water. In surface water and ground water, calcium was the dominant cation, and bicarbonate was the dominant anion. Concentrations of dissolved nitrite and nitrite plus nitrate in surface water and ground water did not exceed the U.S. Environmental Protection Agency maximum contaminant levels of 1 and 10 milligrams per liter for drinking water, respectively. Ammonium plus organic nitrogen in bottom sediment was detected at the highest concentration of any nitrogen species. Median values for most of the dissolved trace elements in surface water and ground water were below the detection levels. Dissolved trace elements in surface water and ground water did not exceed the U.S. Environmental Protection Agency maximum contaminant levels for drinking water. Trace-element concentrations in bottom sediment were similar to trace-element concentrations reported for soils of the western conterminous United States. Several organochlorine pesticides and priority pollutants were detected in surface-water and bottom-sediment samples; however, they did not exceed water-quality standards. Pesticides or priority pollutants were not detected in ground-water samples.

Biogeochemical mercury methylation influenced by reservoir eutrophication, Salmon Falls Creek Reservoir, Idaho, USA

USGS Publications Warehouse

Gray, J.E.; Hines, M.E.

2009-01-01

Salmon Falls Creek Reservoir (SFCR) in southern Idaho has been under a mercury (Hg) advisory since 2001 as fish in this reservoir contain elevated concentrations of Hg. Concentrations of total Hg (HgT) and methyl-Hg (MeHg) were measured in reservoir water, bottom sediment, and porewater to examine processes of Hg methylation at the sediment/water interface in this reservoir. Rates of Hg methylation and MeHg demethylation were also measured in reservoir bottom sediment using isotopic tracer techniques to further evaluate methylation of Hg in SFCR. The highest concentrations for HgT and MeHg in sediment were generally found at the sediment/water interface, and HgT and MeHg concentrations declined with depth. Porewater extracted from bottom sediment contained highly elevated concentrations of HgT ranging from 11-230??ng/L and MeHg ranging from 0.68-8.5??ng/L. Mercury methylation was active at all sites studied. Methylation rate experiments carried out on sediment from the sediment/water interface show high rates of Hg methylation ranging from 2.3-17%/day, which is significantly higher than those reported in other Hg contaminant studies. Using porewater MeHg concentrations, we calculated an upward diffusive MeHg flux of 197??g/year for the entire reservoir. This sediment derived MeHg is delivered to the overlying SFCR water column, and eventually transferred to biota, such as fish. This study indicates that methylation of Hg is highly influenced by the hypolimnetic and eutrophic conditions in SFCR.

Transfer of radionuclides from high polluted bottom sediments to marine organisms through benthic food chain in post Fukushima period

NASA Astrophysics Data System (ADS)

Bezhenar, Roman; Jung, Kyung Tae; Maderich, Vladimir; Willemsen, Stefan; de With, Govert; Qiao, Fangli

2015-04-01

A catastrophic earthquake and tsunami occurred on March 11, 2011 and severely damaged the Fukushima Daiichi Nuclear Power Plant (FDNPP) that resulted in an uncontrolled release of radioactivity into air and ocean. Around 80% of the radioactivity released due to the FDNPP accident in March-April 2011 was either directly discharged into the ocean or deposited onto the ocean surface from the atmosphere. A large amount of long-lived radionuclides (mainly Cs-137) were released into the environment. The concentration of radionuclides in the ocean reached a maximum in mid-April of 2011, and then gradually decreased. From 2011 the concentration of Cs-137 in water essentially fell except the area around the FDNPP where leaks of contaminated water are continued. However, in the bottom sediment high concentrations of Cs-137 were found in the first months after the accident and slowly decreased with time. Therefore, it should be expected that a time delay is found of sediment-bound radionuclides in marine organisms. For the modeling of radionuclide transfer from highly polluted bottom sediments to marine organisms the dynamical food chain model BURN-POSEIDON (Heling et al, 2002; Maderich et al., 2014) was extended. In this model marine organisms are grouped into a limited number of classes based on their trophic level and type of species. These include: phytoplankton, zooplankton, fishes (two types: piscivorous and non-piscivorous), crustaceans, and molluscs for pelagic food chain and bottom sediment invertebrates, demersal fishes and bottom predators for benthic food chain and whole water column predators feeding by pelagial and benthic fishes. Bottom invertebrates consume organic parts of bottom sediments with adsorbed radionuclides which then migrate through the food chain. All organisms take radionuclides directly from water as well as via food. In fishes where radioactivity is not homogeneously distributed over all tissues of the organism, it is assumed that radionuclide accumulates in a specific tissue called target tissue. This tissue (bone, flesh, stomach, and organs) controls the overall elimination rate of the nuclide in the organism. The model prediction for the coastal area around the FDNPP agree well with observations. In addition the effects from the Chernobyl accident on the Baltic Sea are modelled and these results also are in good agreement with available data. These results demonstrate the importance of the benthic food chain in long-term transfer of radionuclides from high polluted bottom sediments to the marine organisms. The developed model can be applied for different regions of the World Ocean.

Physical habitat dynamics in four side-channel chutes, lower Missouri River

USGS Publications Warehouse

Jacobson, Robert B.; Johnson, Harold E.; Laustrup, Mark S.; D'Urso, Gary J.; Reuter, Joanna M.

2004-01-01

Construction of the side-channel chutes has become a popular means to rehabilitate habitate of the Lower Missouri River. We studied various aspects of hydrology, hydraulics, and geomorphology of four side-channel chutes to document a range of existing conditions in the Lower Missouri River. The Cranberry Bend side-channel chute has existed for at least 40 years and is an example of a persistent, minimally engineered chute. The Lisbon Bottom side-channel chute is a young chute, created by extreme floods during 1993-1996, and allowed to evolve with minimum engineering of inlet and outlet structures. The Hamburg Bend and North Overton Bottom side-channel chutes were constructed in 1996 and 2000, respectively, as part of the Missouri River Bank Stabilization and navigation Fish and Wildlife Mitigation Project. These side-channel chutes provide increased areas of sandbars and shallow, slow water -- habitats thought to be substantially diminished in the modern Missouri River. Depths and velocities measured in side-channel chutes are also present in the main channel, but the chutes provide more areas of slow, shallow water and they increase the range of discharges over which shallow, slow water is present. The 3.6 km long Lisbon Bottom chute provides as much as 50% of the entire shallow water habitat that exists in the encompassing 15 km reach of the river. At Cranberry Bend and Lisbon Bottom, the side-channel chutes provided 10-40% of the availabile sandbar area in the reach, depending on discharge. Each of the side-channel chutes shows evidence of continuing erosion and deposition. The longevity and the Cranberry Bend chute attests to dynamic stability -- that is, a chute that maintains form and processes while shifting in position. The Hamburg chute similarly shows evidence of lateral movement and construction of flood plain to compensate for erosion. The Lisbon Bottom chute -- the most intensively studied chute -- appears to have achieved an equilibrium width and continues to migrate slowly; however, evidence of aggradation indicates that the chute has not reached an ultimate form, and may be continuing to adjust to altered hydrology and sediment availability. The North Overton Bottoms chute is the newest in the study. In its originally constructed form, the North Overton Bottoms pilot chute was extremely stable, even while being subjected to two floods in excess of 2-year recurrence interval and after accumulating large, potentially destabilizing large woody debris jams. Ongoing adaptive re-engineering of the North Overton Bottoms chute has prevented assessment of how the chute might have adjusted its form in the absence of intervention.

Testing of the 4SM Method in the Gulf of California Suggests Field Data Are not Needed to Derive Satellite Bathymetry

PubMed Central

Morel, Yann; Waddington, Andrew; Lopez-Calderon, Jorge; Cadena-Roa, Marco; Blanco-Jarvio, Anidia

2017-01-01

Satellite-derived bathymetry methods over coastal areas were developed to deliver basic and useful bathymetry information. However, the process is not straightforward, the main limitation being the need for field data. The Self-calibrated Spectral Supervised Shallow-water Modeler (4SM) method was tested to obtain coastal bathymetry without the use of any field data. Using Landsat-8 multispectral images from 2013 to 2016, a bathymetric time series was produced. Groundtruthed depths and an alternative method, Stumpf’s Band Ratio Algorithm, were used to verify the results. Retrieved (4SM) vs groundtruthed depths scored an average r2 (0.90), and a low error (RMSE = 1.47 m). 4SM also showed, over the whole time series, the same average accuracy of the control method (40%). Advantages, limitations and operability under complex atmosphere and water column conditions, and high and low-albedo bottom processing capabilities of 4SM are discussed. In conclusion, the findings suggest that 4SM is as accurate as the commonly used Stumpf’s method, the only difference being the independence of 4SM from previous field data, and the potential to deliver bottom spectral characteristics for further modeling. 4SM thus represents a significant advance in coastal remote sensing potential to obtain bathymetry and optical properties of the marine bottom. PMID:28973993

Southern Ocean Response to NADW Changes

NASA Technical Reports Server (NTRS)

Rind, David; Schmidt, G.; Russell, G.; deMenocal, P.; Hansen, James E. (Technical Monitor)

2000-01-01

The possibility of North Atlantic Deep Water (NADW) changes in both past and future climates has raised the issue of how the Southern Ocean would respond. Recent experiments with the GISS coupled atmosphere-ocean model have shown that a "bipolar see-saw" between NADW production and Antarctic Bottom Water (AABW) production in the Weddell Sea can occur in conjunction with freshening of the North Atlantic. However, this effect operates not through a slow ocean response but via a rapid atmospheric mechanism. As NADW reduces, colder temperatures in the North Atlantic, and Northern Hemisphere in general, are associated with higher surface pressure (increased atmospheric mass). Reduced mass in the Southern Hemisphere occurs in response, with lower pressure over the South Pole (an EOF #1 effect, the "high phase" of the Antarctic Oscillation).The lower pressure is associated with stronger west winds that generate an intensified Antarctic Circumpolar Current (ACC), which leads to longitudinal heat divergence in the South Atlantic (and heat convergence in the Southern Indian Ocean). Colder temperatures in the Weddell Sea region lead to sea ice growth, increased salinity and surface water density, and greater Weddell Sea Bottom Water production. Increased poleward transport of heat occurs in the South Atlantic in conjunction with increased bottom water production, but its convergence at high latitudes is not sufficient to offset the longitudinal heat divergence due to the intensified ACC. The colder temperatures at high latitudes in the South Atlantic increase the latitudinal temperature gradient, baroclinic instability, eddy energy and eddy poleward transport of momentum, helping to maintain the lower pressure over the pole in an interactive manner. The heat flux convergence in the Indian Ocean provides a warming tendency in that region, and overall global production of AABW remains unchanged. These results have implications for the interpretation of the ice core records of the last deglaciation, but may also be relevant for changes during the Holocene and perhaps even in response to increased CO2 forcing,

Vertical segregation among pathways mediating nitrogen loss (N2 and N2O production) across the oxygen gradient in a coastal upwelling ecosystem

NASA Astrophysics Data System (ADS)

Galán, Alexander; Thamdrup, Bo; Saldías, Gonzalo S.; Farías, Laura

2017-10-01

The upwelling system off central Chile (36.5° S) is seasonally subjected to oxygen (O2)-deficient waters, with a strong vertical gradient in O2 (from oxic to anoxic conditions) that spans a few metres (30-50 m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N2 and/or N2O, were studied using 15N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. Incubations were developed using water retrieved from the oxycline (25 m depth) and bottom waters (85 m depth) over the continental shelf off Concepción, Chile. Results of 15N-labelled incubations revealed higher N removal activity during the austral summer, with denitrification as the dominant N2-producing pathway, which occurred together with anammox at all times. Interestingly, in both spring and summer maximum potential N removal rates were observed in the oxycline, where a greater availability of oxygen was observed (maximum O2 fluctuation between 270 and 40 µmol L-1) relative to the hypoxic bottom waters ( < 20 µmol O2 L-1). Different pathways were responsible for N2O produced in the oxycline and bottom waters, with ammonium oxidation and dissimilatory nitrite reduction, respectively, as the main source processes. Ammonium produced by dissimilatory nitrite reduction to ammonium (DNiRA) could sustain both anammox and nitrification rates, including the ammonium utilized for N2O production. The temporal and vertical variability of δ15N-NO3- confirms that multiple N-cycling processes are modulating the isotopic nitrate composition over the shelf off central Chile during spring and summer. N removal processes in this coastal system appear to be related to the availability and distribution of oxygen and particles, which are a source of organic matter and the fuel for the production of other electron donors (i.e. ammonium) and acceptors (i.e. nitrate and nitrite) after its remineralization. These results highlight the links between several pathways involved in N loss. They also establish that different mechanisms supported by alternative N substrates are responsible for substantial accumulation of N2O, which are frequently observed as hotspots in the oxycline and bottom waters. Considering the extreme variation in oxygen observed in several coastal upwelling systems, these findings could help to understand the ecological and biogeochemical implications due to global warming where intensification and/or expansion of the oceanic OMZs is projected.

An analytical two-flow model to simulate the distribution of irradiance in coastal waters with a wind-roughed surface and bottom reflectance

NASA Astrophysics Data System (ADS)

Ma, Wei-Ming

1997-06-01

An analytical two-flow model is derived from the radiative transfer equation to simulate the distribution of irradiance in coastal waters with a wind-roughed surface and bottom reflectance. The model utilizes unique boundary conditions, including the surface slope of the downwelling and upwelling irradiance as well as the influence of wind and bottom reflectance on simulated surface reflectance. The developed model provides a simple mathematical concept for understanding the irradiant light flux and associated processes in coastal or fresh water as well as turbid estuarine waters. The model is applied to data from the Banana River and coastal Atlantic Ocean water off the east coast of central Florida, USA. The two-flow irradiance model is capable of simulating realistic above-surface reflectance signatures under wind-roughened air-water surface given realistic input parameters including a specular flux conversion coefficient, absorption coefficient, backscattering coefficient, atmospheric visibility, bottom reflectance, and water depth. The root-mean-squared error of the calculated above-surface reflectances is approximately 3% in the Banana River and is less than 15% in coastal Atlantic Ocean off the east of Florida. Result of the subsurface reflectance sensitivity analysis indicates that the specular conversion coefficient is the most sensitive parameter in the model, followed by the beam attenuation coefficient, absorption coefficient, water depth, backscattering coefficient, specular irradiance, diffuse irradiance, bottom reflectance, and wind speed. On the other hand, result of the above-surface reflectance sensitivity analysis indicates that the wind speed is the most important parameter, followed by bottom reflectance, attenuation coefficient, water depth, conversion coefficient, specular irradiance, downwelling irradiance, absorption coefficient, and backscattering coefficient. Model results depend on the accuracy of these parameters to a large degree and more important the water depth and value of the bottom reflectance. The results of this work indicates little change of subsurface or in-water reflectances, due to variations of wind speed and observation angle. Simulations of the wind effect on the total downwelling irradiance from the two- flow model indicates that the total downwelling irradiance just below a wind-roughened water surface increases to about 1% of the total downwelling irradiance on a calm water surface when the sun is near zenith and increases to about 3% when the sun is near the horizon. This analytically based model, solved or developed utilizing the unique boundary conditions, can be applied to remote sensing of oceanic upper mixed layer dynamics, plant canopies, primary production, and shallow water environments with different bottom type reflectances. Future applications may include determining effects of sediment resuspension of bottom sediments in the bottom boundary layer on remotely sensed data.

Water-quality assessment of the Potomac River Basin: analysis of available pesticide data, 1972-1990

USGS Publications Warehouse

Zappia, Humbert; Fisher, Gary T.

1997-01-01

A study of available data for the period from 1972 to 1990 was conducted to characterize the occurrence and distribution of pesticides in sur-face water, bottom material, ground water, and fish tissue in the Potomac River Basin. The study was conducted by the Potomac River study unit of the U.S. Geological Survey?s National Water-Quality Assessment (NAWQA) program. Exist-ing data coverage was evaluated to guide future data-collection activities. Data from computer data bases and from published and unpublished reports were obtained from local, State, and Fed-eral agencies in the four Potomac River Basin states and the District of Columbia. Data are available for all environmental media, but geo-graphic and temporal coverage are limited. Clusters of data occur in the north-central parts of the basin, with numerous samples at discrete loca-tions in the Shenandoah and Monocacy River Basins, along the mainstem Potomac River, in the Washington, D.C., area, and in streams along the Potomac Estuary. Much of the available surface-water and bottom-material data are from the ear-lier years of the period of interest, the ground-water data are from the middle years, and the fish-tissue data are distributed over much of the period. Overall, temporal coverage is not sufficient for analysis of trends. Comparisons between different sample media are possible in some areas of the Potomac River Basin, particularly in the northern end of the Great Valley. Residual concentrations of some pesticides have been found in surface water, bottom mate-rial, ground water, and fish tissue. Samples have been analyzed for a total of at least 69 pesticides and related compounds in surface water, bottom material, ground water, and fish tissue. Most con-centrations of the pesticides analyzed during the period from 1972 to 1990 were less than or equal to reporting limits. For surface-water samples, 13 out of 41 pes-ticides and related compounds analyzed had concentrations equal to or greater than the report-ing limits. Compounds reported in surface water included 2,4-D, atrazine, aldrin, chlordane, DDT and related compounds, dieldrin, endrin, lindane, prometone, prometryne, and simazine. For bottom material samples, 19 of 31 pesticides and related compounds analyzed had concentrations equal to or greater than the reporting limits. Compounds reported in bottom material included aldrin, chlor-dane, DDT and related compounds, diazinon, dieldrin, endosulfan, endrin, ethion, heptachlor, heptachlor epoxide, lindane, parathion, and tox-aphene. In ground-water samples, 14 of 39 pesticides and related compounds analyzed had concentrations equal to or greater than the report-ing limits. Compounds reported in ground water included 2,4-D, atrazine, chlordane, cyanazine, DDT and related compounds, diazinon, dieldrin, endosulfan, endrin, heptachlor epoxide, malathion, methyl parathion, simazine. For fish- tissue sam-ples, 30 of the 37 pesticides and related compounds analyzed had concentrations equal to or greater than the reporting limits. Compounds reported included aldrin, chlorpyrifos, dacthal, dieldrin, endrin, HCB, heptachlor, heptachlor epoxide, methoxychlor, mirex, PCA, toxaphene, and those compounds related to chlordane, DDT, and lindane.

Geochemical history of Lake Miccosukee, Florida

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Z.Q.; Donoghue, J.F.; Hess, D.W.

1994-03-01

Lake Miccosukee is a 2,500 hectare karst lake in northwest Florida. The lake draws water from a 65,000 hectare watershed, although groundwater seepage appears to be the principal water source to the lake. Like many of the large lakes of north Florida it periodically drains via sinkholes, becoming nearly dry in the process. The result of the natural drawdowns is a large reduction of the organic matter content of the bottom sediments. The water level in the lake was stabilized after 1954 with the construction of a dike and weir. Drawdowns have been managed since then and have been fewermore » and less drastic. The lake bottom has been exposed for only about six months since 1954. The result has been an increase in aquatic vegetation and a diminishment in fish populations. A set of two dozen sediment cores was analyzed for sedimentation rate (using lead-210 and Cs-137), percent organics, C, N, P and trace metals. The effect of the lake level stabilization appears to be an increase in organic matter deposited in the bottom sediments. Anthropogenic metals, including Hg, Zn, Pb, Cu and V have been found to increase considerably near the tops of the cores, by a factor of two or more over long-term background levels.« less

Classification of bottom composition and bathymetry of shallow waters by passive remote sensing

NASA Astrophysics Data System (ADS)

Spitzer, D.; Dirks, R. W. J.

The use of remote sensing data in the development of algorithms to remove the influence of the watercolumn on upwelling optical signals when mapping the bottom depth and composition in shallow waters. Calculations relating the reflectance spectra to the parameters of the watercolumn and the diverse bottom types are performed and measurements of the underwater reflection coefficient of sandy, mud, and vegetation-type seabottoms are taken. The two-flow radiative transfer model is used. Reflectances within the spectral bands of the Landsat MSS, the Landsat TM, SPOT HVR, and the TIROS-N series AVHRR were computed in order to develop appropriate algorithms suitable for the bottom depth and type mapping. Bottom depth and features appear to be observable down to 3-20 m depending on the water composition and bottom type.

Global view of sea-ice production in polynyas and its linkage to dense/bottom water formation

NASA Astrophysics Data System (ADS)

Ohshima, Kay I.; Nihashi, Sohey; Iwamoto, Katsushi

2016-12-01

Global overturning circulation is driven by density differences. Saline water rejected during sea-ice formation in polynyas is the main source of dense water, and thus sea-ice production is a key factor in the overturning circulation. Due to difficulties associated with in situ observation, sea-ice production and its interannual variability have not been well understood until recently. Methods to estimate sea-ice production on large scales have been developed using heat flux calculations based on satellite microwave radiometer data. Using these methods, we present the mapping of sea-ice production with the same definition and scale globally, and review the polynya ice production and its relationship with dense/bottom water. The mapping demonstrates that ice production rate is high in Antarctic coastal polynyas, in contrast to Arctic coastal polynyas. This is consistent with the formation of Antarctic Bottom Water (AABW), the densest water mass which occupies the abyssal layer of the global ocean. The Ross Ice Shelf polynya has by far the highest ice production in the Southern Hemisphere. The Cape Darnley polynya (65°E-69°E) is found to be the second highest production area and recent observations revealed that this is the missing (fourth) source of AABW. In the region off the Mertz Glacier Tongue (MGT), the third source of AABW, sea-ice production decreased by as much as 40 %, due to the MGT calving in early 2010, resulting in a significant decrease in AABW production. The Okhotsk Northwestern polynya exhibits the highest ice production in the Northern Hemisphere, and the resultant dense water formation leads to overturning in the North Pacific, extending to the intermediate layer. Estimates of its ice production show a significant decrease over the past 30-50 years, likely causing the weakening of the North Pacific overturning. These regions demonstrate the strong linkage between variabilities of sea-ice production and bottom/intermediate water formation. The mapping has also provided surface boundary conditions and validation data of heat- and salt-flux associated with sea-ice formation/melting for various ocean and coupled models.

Measurements in the bottom boundary layer on the Amazon subaqueous delta

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.; Kayen, R.W.; Sternberg, R.W.; Kineke, G.C.; Tate, G.B.

1995-01-01

An instrumented bottom tripod (GEOPROBE) recorded flow and suspended sediment data in the bottom boundary layer above the lower foresets of the Amazon subaqueous delta in 65 m mean water depth in February, 1990. After about two weeks of operation the apparent seafloor at the tripod site rapidly elevated over a 14-hour period by about 44 cm. This sudden change, which was detected by an acoustic altimeter and which caused the loss of signals from the lowermost GEOPROBE current and optical sensors, is though to have been caused by the incursion of a dense bottom layer of fluid mud that migrated downslope from shallower sections of the foresets. The fluid-mud migration across the outer part of the foresets, if a repetitive and occasional process in this region, could be a major mechanism for episodic seaward growth of the delta. Current velocity profiles are used to estimate shear velocities, u*, and roughness lengths, zo, during the first two weeks of measurements. -from Authors

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory; determination of semivolatile organic compounds in bottom sediment by solvent extraction, gel permeation chromatographic fractionation, and capillary-column gas chromatography/mass spectrometry

USGS Publications Warehouse

Furlong, E.T.; Vaught, D.G.; Merten, L.M.; Foreman, W.T.; Gates, Paul M.

1996-01-01

A method for the determination of 79 semivolatile organic compounds (SOCs) and 4 surrogate compounds in soils and bottom sediment is described. The SOCs are extracted from bottom sediment by solvent extraction, followed by partial isolation using high-performance gel permeation chromatography (GPC). The SOCs then are qualitatively identified and quantitative concentrations determined by capillary-column gas chromatography/mass spectrometry (GC/MS). This method also is designed for an optional simultaneous isolation of polychlorinated biphenyls (PCBs) and organochlorine (OC) insecticides, including toxaphene. When OCs and PCBs are determined, an additional alumina- over-silica column chromatography step follows GPC cleanup, and quantitation is by dual capillary- column gas chromatography with electron-capture detection (GC/ECD). Bottom-sediment samples are centrifuged to remove excess water and extracted overnight with dichloromethane. The extract is concentrated, centrifuged, and then filtered through a 0.2-micrometer polytetrafluoro-ethylene syringe filter. Two aliquots of the sample extract then are quantitatively injected onto two polystyrene- divinylbenzene GPC columns connected in series. The SOCs are eluted with dichloromethane, a fraction containing the SOCs is collected, and some coextracted interferences, including elemental sulfur, are separated and discarded. The SOC-containing GPC fraction then is analyzed by GC/MS. When desired, a second aliquot from GPC is further processed for OCs and PCBs by combined alumina-over-silica column chromatography. The two fractions produced in this cleanup then are analyzed by GC/ECD. This report fully describes and is limited to the determination of SOCs by GC/MS.

Demersal and larval fish assemblages in the Chukchi Sea

NASA Astrophysics Data System (ADS)

Norcross, Brenda L.; Holladay, Brenda A.; Busby, Morgan S.; Mier, Kathryn L.

2010-01-01

A multidisciplinary research cruise was conducted in the Chukchi Sea in summer 2004 during which we investigated assemblages of small demersal fishes and ichthyoplankton and the water masses associated with these assemblages. This study establishes a baseline of 30 demersal fish and 25 ichthyoplankton taxa in US and Russian waters of the Chukchi Sea. Presence/absence of small demersal fish clustered into four assemblages: Coastal Fishes, Western Chukchi Fishes, South Central Chukchi Fishes, and North Central Chukchi Fishes. Habitats occupied by small demersal fishes were characterized by sediment type, bottom salinity, and bottom temperature. Abundance of ichthyoplankton grouped into three assemblages with geographical extent similar to that of the bottom assemblages, except that there was a single assemblage for Central Chukchi Fishes. Water-column temperature and salinity characterized ichthyoplankton habitats. Three water masses, Alaska Coastal Water, Bering Sea Water, and Winter Water, were identified from both bottom and depth-averaged water-column temperature and salinity. A fourth water mass, Resident Chukchi Water, was identified only in the bottom water. The water mass and habitat characteristics with which demersal and larval fish assemblages were associated create a baseline to measure anticipated effects of climate change that are expected to be most severe at high latitudes. Monitoring fish assemblages could be a tool for assessing the effects of climate change. Climate-induced changes in distributions of species would result in a restructuring of fish assemblages in the Chukchi Sea.

Laboratory measurements of physical, chemical, and optical characteristics of Lake Chicot sediment waters

NASA Technical Reports Server (NTRS)

Witte, W. G.; Whitlock, C. H.; Usry, J. W.; Morris, W. D.; Gurganus, E. A.

1981-01-01

Reflectance, chromaticity, diffuse attenuation, beam attenuation, and several other physical and chemical properties were measured for various water mixtures of lake bottom sediment. Mixture concentrations range from 5 ppm to 700 ppm by weight of total suspended solids in filtered deionized tap water. Upwelled reflectance is a nonlinear function of remote sensing wave lengths. Near-infrared wavelengths are useful for monitoring highly turbid waters with sediment concentrations above 100 ppm. It is found that both visible and near infrared wavelengths, beam attenuation correlates well with total suspended solids ranging over two orders of magnitude.

Science to support adaptive habitat management: Overton Bottoms North Unit, Big Muddy National Fish and Wildlife Refuge, Missouri [Volumes 1-6

USGS Publications Warehouse

Jacobson, Robert B.

2006-01-01

Extensive efforts are underway along the Lower Missouri River to rehabilitate ecosystem functions in the channel and flood plain. Considerable uncertainty inevitably accompanies ecosystem restoration efforts, indicating the benefits of an adaptive management approach in which management actions are treated as experiments, and results provide information to feed back into the management process. The Overton Bottoms North Unit of the Big Muddy National Fish and Wildlife Refuge is a part of the Missouri River Fish and Wildlife Habitat Mitigation Project. The dominant management action at the Overton Bottoms North Unit has been excavation of a side-channel chute to increase hydrologic connectivity and to enhance shallow, slow current-velocity habitat. The side-channel chute also promises to increase hydrologic gradients, and may serve to alter patterns of wetland inundation and vegetation community growth in undesired ways. The U.S. Geological Survey's Central Region Integrated Studies Program (CRISP) undertook interdisciplinary research at the Overton Bottoms North Unit in 2003 to address key areas of scientific uncertainty that were highly relevant to ongoing adaptive management of the site, and to the design of similar rehabilitation projects on the Lower Missouri River. This volume presents chapters documenting the surficial geologic, topographic, surface-water, and ground-water framework of the Overton Bottoms North Unit. Retrospective analysis of vegetation community trends over the last 10 years is used to evaluate vegetation responses to reconnection of the Overton Bottoms North Unit to the river channel. Quasi-experimental analysis of cottonwood growth rate variation along hydrologic gradients is used to evaluate sensitivity of terrestrial vegetation to development of aquatic habitats. The integrated, landscape-specific understanding derived from these studies illustrates the value of scientific information in design and management of rehabilitation projects.

Life cycle based risk assessment of recycled materials in roadway construction.

PubMed

Carpenter, A C; Gardner, K H; Fopiano, J; Benson, C H; Edil, T B

2007-01-01

This paper uses a life-cycle assessment (LCA) framework to characterize comparative environmental impacts from the use of virgin aggregate and recycled materials in roadway construction. To evaluate site-specific human toxicity potential (HTP) in a more robust manner, metals release data from a demonstration site were combined with an unsaturated contaminant transport model to predict long-term impacts to groundwater. The LCA determined that there were reduced energy and water consumption, air emissions, Pb, Hg and hazardous waste generation and non-cancer HTP when bottom ash was used in lieu of virgin crushed rock. Conversely, using bottom ash instead of virgin crushed rock increased the cancer HTP risk due to potential leachate generation by the bottom ash. At this scale of analysis, the trade-offs are clearly between the cancer HTP (higher for bottom ash) and all of the other impacts listed above (lower for bottom ash). The site-specific analysis predicted that the contaminants (Cd, Cr, Se and Ag for this study) transported from the bottom ash to the groundwater resulted in very low unsaturated zone contaminant concentrations over a 200 year period due to retardation in the vadose zone. The level of contaminants predicted to reach the groundwater after 200 years was significantly less than groundwater maximum contaminant levels (MCL) set by the US Environmental Protection Agency for drinking water. Results of the site-specific contaminant release estimates vary depending on numerous site and material specific factors. However, the combination of the LCA and the site specific analysis can provide an appropriate context for decision making. Trade-offs are inherent in making decisions about recycled versus virgin material use, and regulatory frameworks should recognize and explicitly acknowledge these trade-offs in decision processes.

Vertical migration and nighttime distribution of adult bloaters in Lake Michigan

USGS Publications Warehouse

TeWinkel, Leslie M.; Fleischer, Guy W.

1999-01-01

The vertical migration and nighttime vertical distribution of adult bloaters Coregonus hoyi were investigated during late summer in Lake Michigan using acoustics simultaneously with either midwater or bottom trawling. Bloaters remained on or near bottom during the day. At night, bloaters were distributed throughout 30-65 m of water, depending on bottom depth. Shallowest depths of migration were not related to water temperature or incident light. Maximum distances of migration increased with increasing bottom depth. Nighttime midwater densities ranged from 0.00 to 6.61 fish/1,000 mA? and decreased with increasing bottom depth. Comparisons of length distributions showed that migrating and nonmigrating bloaters did not differ in size. However, at most sites, daytime bottom catches collected a greater proportion of larger individuals compared with nighttime midwater or bottom catches. Mean target strengths by 5-m strata indicated that migrating bloaters did not stratify by size in the water column at night. Overall, patterns in frequency of empty stomachs and mean digestive state of prey indicated that a portion of the bloater population fed in the water column at night. Bloater diet composition indicated both midwater feeding and bottom feeding. In sum, although a portion of the bloater population fed in the water column at night, bloaters were not limited to feeding at this time. This research confirmed that bloaters are opportunistic feeders and did not fully support the previously proposed hypothesis that bloater vertical migration is driven by the vertically migrating macroinvertebrate the opossom shrimp Mysis relicta.

33 CFR 401.28 - Speed limits.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 33 Navigation and Navigable Waters 3 2011-07-01 2011-07-01 false Speed limits. 401.28 Section 401... TRANSPORTATION SEAWAY REGULATIONS AND RULES Regulations Seaway Navigation § 401.28 Speed limits. (a) The maximum speed over the bottom for a vessel of more than 12 m in overall length shall be regulated so as not to...

33 CFR 401.28 - Speed limits.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Speed limits. 401.28 Section 401... TRANSPORTATION SEAWAY REGULATIONS AND RULES Regulations Seaway Navigation § 401.28 Speed limits. (a) The maximum speed over the bottom for a vessel of more than 12 m in overall length shall be regulated so as not to...

Characterizing wave- and current- induced bottom shear stress: U.S. middle Atlantic continental shelf

USGS Publications Warehouse

Dalyander, P. Soupy; Butman, Bradford; Sherwood, Christopher R.; Signell, Richard P.; Wilkin, John L.

2013-01-01

Waves and currents create bottom shear stress, a force at the seabed that influences sediment texture distribution, micro-topography, habitat, and anthropogenic use. This paper presents a methodology for assessing the magnitude, variability, and driving mechanisms of bottom stress and resultant sediment mobility on regional scales using numerical model output. The analysis was applied to the Middle Atlantic Bight (MAB), off the U.S. East Coast, and identified a tidally-dominated shallow region with relatively high stress southeast of Massachusetts over Nantucket Shoals, where sediment mobility thresholds are exceeded over 50% of the time; a coastal band extending offshore to about 30 m water depth dominated by waves, where mobility occurs more than 20% of the time; and a quiescent low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the “Mud Patch”. The regional high in stress and mobility over Nantucket Shoals supports the hypothesis that fine grain sediment winnowed away in this region maintains the Mud Patch to the southwest. The analysis identified waves as the driving mechanism for stress throughout most of the MAB, excluding Nantucket Shoals and sheltered coastal bays where tides dominate; however, the relative dominance of low-frequency events varied regionally, and increased southward toward Cape Hatteras. The correlation between wave stress and local wind stress was lowest in the central MAB, indicating a relatively high contribution of swell to bottom stress in this area, rather than locally generated waves. Accurate prediction of the wave energy spectrum was critical to produce good estimates of bottom shear stress, which was sensitive to energy in the long period waves.

Observations of pockmark flow structure in Belfast Bay, Maine, Part 1: current-induced mixing

USGS Publications Warehouse

Fandel, Christina L.; Lippmann, Thomas C.; Irish, James D.; Brothers, Laura L.

2017-01-01

Field observations of current profiles and temperature, salinity, and density structure were used to examine vertical mixing within two pockmarks in Belfast Bay, Maine. The first is located in 21 m water depth (sea level to rim), nearly circular in shape with a 45 m rim diameter and 12 m rim-to-bottom relief. The second is located in 25 m water depth, more elongated in shape with an approximately 80 m (36 m) major (minor) axis length at the rim, and 17 m relief. Hourly averaged current profiles were acquired from bottom-mounted acoustic Doppler current profilers deployed on the rim and center of each pockmark over successive 42 h periods in July 2011. Conductivity–temperature–depth casts at the rim and center of each pockmark show warmer, fresher water in the upper water column, evidence of both active and fossil thermocline structure 5–8 m above the rim, and well-mixed water below the rim to the bottom. Vertical velocities show up- and down-welling events that extend into the depths of each pockmark. An observed temperature change at both the rim and center occurs coincident with an overturning event below the rim, and suggests active mixing of the water column into the depths of each pockmark. Vertical profiles of horizontal velocities show depth variation at both the center and rim consistent with turbulent logarithmic current boundary layers, and suggest that form drag may possibly be influencing the local flow regime. While resource limitations prevented observation of the current structure and water properties at a control site, the acquired data suggest that active mixing and overturning within the sampled pockmarks occur under typical benign conditions, and that current flows are influenced by upstream bathymetric irregularities induced by distant pockmarks.

Satellite detection of phytoplankton export from the mid-Atlantic Bight during the 1979 spring bloom

NASA Technical Reports Server (NTRS)

Walsh, J. J.; Dieterle, D. A.; Esaias, W. E.

1986-01-01

Analysis of Coastal Zone Color Scanner (CZCS) imagery confirms shipboard and in situ moored fluorometer observations of resuspension of near-bottom chlorophyll within surface waters (1 to 10 m) by northwesterly wind events in the mid-Atlantic Bight. As much as 8 to 16 micrograms chl/l are found during these wind events from March to May, with a seasonal increase of algal biomass until onset of stratification of the water column. Rapid sinking or downwelling apparently occurs after subsequent wind events, however, such that the predominant surface chlorophyll pattern is approx. 0.5 to 1.5 micrograms/l over the continental shelf during most of the spring bloom. Perhaps half of the chlorophyll increase observed by satellite during a wind resuspension event represents in-situ production during the 4 to 5 day interval, with the remainder attributed to accumulation of algal biomass previously produced and temporarily stored within near-bottom water. Present calculations suggest that about 10% of the primary production of the spring bloom may be exported as ungrazed phytoplankton carbon from mid-Atlantic shelf waters to those of the continental slope.

Evaluation of concrete incorporating bottom ash as a natural aggregates replacement.

PubMed

Andrade, L B; Rocha, J C; Cheriaf, M

2007-01-01

A study on the incorporation of coal bottom ash from thermoelectric power stations as a substitute material for natural sand in the production of concrete is here presented. The normally coarse, fused, glassy texture of bottom ash makes it an ideal substitute for natural aggregates. The use of bottom ash in concrete presents several technical challenges: the physical and mineralogical characteristics of the bottom ash; the effect on water demand and the participation on cements hydratation. In the production of the concrete, substitutions in volume were used. Two different ways to employ bottom ash were used to make up the mix proportions: one considering the natural humidity present in the porous particles and the other not considering it, seeking to maintain the same strength. These considerations are fundamental given that the process of bottom ash extraction is carried out through moisture. Mechanical tests by compressive strength were performed and the elastic modulus was determined. An analysis of the influence of bottom ash in the formation of pores was carried out through tests for the water loss by air drying and water uptake by capillary absorption. The results show that the higher the bottom ash contents in the concrete, the worse the performance regarding moisture transport. However, for one bottom ash concrete type, the mechanical properties were maintained.

Habitat selection models for Pacific sand lance (Ammodytes hexapterus) in Prince William Sound, Alaska

USGS Publications Warehouse

Ostrand, William D.; Gotthardt, Tracey A.; Howlin, Shay; Robards, Martin D.

2005-01-01

We modeled habitat selection by Pacific sand lance (Ammodytes hexapterus) by examining their distribution in relation to water depth, distance to shore, bottom slope, bottom type, distance from sand bottom, and shoreline type. Through both logistic regression and classification tree models, we compared the characteristics of 29 known sand lance locations to 58 randomly selected sites. The best models indicated a strong selection of shallow water by sand lance, with weaker association between sand lance distribution and beach shorelines, sand bottoms, distance to shore, bottom slope, and distance to the nearest sand bottom. We applied an information-theoretic approach to the interpretation of the logistic regression analysis and determined importance values of 0.99, 0.54, 0.52, 0.44, 0.39, and 0.25 for depth, beach shorelines, sand bottom, distance to shore, gradual bottom slope, and distance to the nearest sand bottom, respectively. The classification tree model indicated that sand lance selected shallow-water habitats and remained near sand bottoms when located in habitats with depths between 40 and 60 m. All sand lance locations were at depths <60 m and 93% occurred at depths <40 m. Probable reasons for the modeled relationships between the distribution of sand lance and the independent variables are discussed.

Role of cold water and beta-effect in the formation of the East Korean Warm Current in the East/Japan Sea: a numerical experiment

NASA Astrophysics Data System (ADS)

Kim, Yong-Yub; Cho, Yang-Ki; Kim, Young Ho

2018-06-01

The contributions of bottom cold water and planetary β-effect to the formation of the East Korean Warm Current (EKWC), the western boundary current in the East/Japan Sea (EJS), were evaluated using an idealized three-dimensional numerical model. The model results suggest that the bottom cold water and, to a lesser extent, the planetary β-effect both contribute to the formation of the EKWC. The cold water functions as the bottom of the upper layer, to control the EKWC via conservation of potential vorticity. It is known that cold waters, such as the North Korean Cold Water and Korea Strait Bottom Cold Water often observed during summer along the southwestern coast of the EJS, originate from the winter convection in the northern area. Observational studies consistently show that the EKWC strengthens in summer when the cold water extends further south along the western boundary.

A numerical analysis of biogeochemical controls with physical modulation on hypoxia during summer in the Pearl River estuary

NASA Astrophysics Data System (ADS)

Wang, Bin; Hu, Jiatang; Li, Shiyu; Liu, Dehong

2017-06-01

A three-dimensional (3-D) physical-biogeochemical coupled model was applied to explore the mechanisms controlling the dissolved oxygen (DO) dynamics and bottom hypoxia during summer in the Pearl River estuary (PRE). By using the numerical oxygen tracers, we proposed a new method (namely the physical modulation method) to quantify the contributions of boundary conditions and each source and sink process occurring in local and adjacent waters to the DO conditions. A mass balance analysis of DO based on the physical modulation method indicated that the DO conditions at the bottom layer were mainly controlled by the source and sink processes, among which the sediment oxygen demand (SOD) at the water-sediment interface and the re-aeration at the air-sea interface were the two primary processes determining the spatial extent and duration of bottom hypoxia in the PRE. The SOD could cause a significant decrease in the bottom DO concentrations (averaged over July-August 2006) by over 4 mg L-1 on the shelf off the Modaomen sub-estuary, leading to the formation of a high-frequency zone of hypoxia (HFZ). However, the hypoxia that occurred in the HFZ was intermittent and distributed in a small area due to the combined effects of re-aeration and photosynthesis, which behaved as sources for DO and offset a portion of the DO consumed by SOD. The bottom DO concentrations to the west of the lower Lingdingyang Bay (i.e. the western shoal near Qi'ao Island) were also largely affected by high SOD, but there was no hypoxia occurring there because of the influence of re-aeration. Specifically, re-aeration could lead to an increase in the bottom DO concentrations by ˜ 4.8 mg L-1 to the west of the lower Lingdingyang Bay. The re-aeration led to a strong vertical DO gradient between the surface and the lower layers. As a result, the majority (˜ 89 %) of DO supplemented by re-aeration was transported to the lower layers through vertical diffusion and ˜ 28 % reached the bottom eventually. Additional numerical experiments showed that turning off re-aeration could lead to an expansion of the hypoxic area from 237 to 2203 km2 and result in persistent hypoxia (hypoxic frequency > 80 %) to the west of the lower Lingdingyang Bay. Compared to re-aeration and SOD, photosynthesis and water column respiration had relatively small impacts on the DO conditions; turning off these two processes increased the hypoxic area to 591 km2. In summary, our study explicitly elucidated the interactive impacts of physical and biogeochemical processes on the DO dynamics in the PRE, which is critical to understanding hypoxia in this shallow and river-dominated estuarine system.

A Laboratory Model of a Cooled Continental Shelf

DTIC Science & Technology

1993-06-01

26 Abstract A laboratory model of wintertime cooling over a continental shelf has a water surface cooled by air in an annular rotating...singular point where Froude number u/(g’hl)1/2 equaled a given value and flowed out along the bottom. In this formula, u is velocity of the water onto...support cross-shelf geostrophic currents. To accomplish this, an annular geometry was used. A cylindrical tank was fitted with a shallow but wide

The removal of particle-reactive radionuclides in shallow water: Bottom scavenging versus particle settling of iodine-131 and beryllium-7.

PubMed

Montenero, Michael P; Dilbone, Elizabeth K; Waples, James T

2017-10-01

In pelagic waters, the removal of particle-reactive radionuclides is controlled by nuclide sorption to particles and subsequent settling by gravity. However, in shallow nearshore waters, the dominant mechanism of nuclide scavenging is not so clear. Understanding how particle-reactive radionuclides are scavenged from the water column is critical if these tracers are to be used as proxies of particle flux in shallow aquatic systems. In this study, we present evidence that the removal of particle-reactive radionuclides in nearshore and turbulent waters is primarily controlled by bottom scavenging. Specifically, we measured both water column and bottom sediment activities of sewage-sourced iodine-131 ( 131 I, t ½ = 8.02 days) and atmospherically-sourced beryllium-7 ( 7 Be, t ½ = 53.3 days) in a semi-enclosed harbor. We show that the water column 7 Be/ 131 I flux ratio that is required to sustain observed harbor bottom inventories of both nuclides is incongruent with 7 Be/ 131 I activity ratios on water column particles, and (2) 131 I and 7 Be derived mass fluxes of particulate matter to the harbor bottom are in concordance with each other and independently made estimates of river sediment loading to the harbor only when bottom scavenging of both particle-bound and dissolved (<0.7 μm) nuclide fractions are considered. Copyright © 2017 Elsevier Ltd. All rights reserved.

Deep-sea macroplankton distribution (at 400 to 2300 m) in the northwestern Mediterranean in relation to environmental factors

NASA Astrophysics Data System (ADS)

Cartes, J. E.; Fanelli, E.; López-Pérez, C.; Lebrato, M.

2013-03-01

Changes in the composition and biomass distribution of deep-living zooplankton over wide gradients of depth (400-2300 m) and longitude (~ 180 km) have been analyzed in the Balearic Basin (western Mediterranean), seeking the environmental variables responsible for these changes. Zooplankton tends to aggregate at different levels of the water column (forming Deep Scattering Layers, DSL) and in the Benthic Boundary Layer (BBL). Macrozooplankton biomass and composition were analyzed along a transect performed in July 2010 in midwater (between ~ 350 and 450 m) and near the bottom (at ~ 5-200 mab), over soundings of 450-2263 m, including the top of Valencia Seamount (at ~ 40° 25' N-02° 42' E, 1076 m). Zooplankton changed significantly in composition at the mesoscale (~ 180 km) in both the DSL and the BBL. Siphonophores and calanoid copepods were the most dominant deep zooplankton taxa, calanoids reaching higher abundance in the BBL (1761-5177 individuals/1000 m3) than in the DSL (1568-1743 individuals/1000 m3). There was a significant increase in near-bottom zooplankton biomass over the middle slope, at 1000-1300 m, linked to an increase in scyphozoans and siphonophores (Lensia spp. and Abylopsis tetragona) with peaks of 1.5-2.0 gWW/1000 m3. The peak of near-bottom zooplankton at 1000-1300 m coincided with the lowest temperatures (13.08 °C) and maximum O2 concentration (4.40 ml/l) near the bottom and below 1000 m with higher records in near-bottom turbidity. Gelatinous zooplankton are the main prey in the diet of the demersal fish Alepocephalus rostratus in the western Mediterranean, fish responsible for the peak of megafauna biomass reported at around 1200-1400 m in the deep Mediterranean and at similar depths in other oceanic areas (e.g. the NW Atlantic). We suggest that deep-sea environmental conditions can govern peaks of near-bottom zooplankton, as well as influence the structure of the demersal fish community.

Marine Geophysical Investigation of Selected Sites in Bridgeport Harbor, Connecticut, 2006

USGS Publications Warehouse

Johnson, Carole D.; White, Eric A.

2007-01-01

A marine geophysical investigation was conducted in 2006 to help characterize the bottom and subbottom materials and extent of bedrock in selected areas of Bridgeport Harbor, Connecticut. The data will be used by the U.S. Army Corps of Engineers in the design of confined aquatic disposal (CAD) cells within the harbor to facilitate dredging of the harbor. Three water-based geophysical methods were used to evaluate the geometry and composition of subsurface materials: (1) continuous seismic profiling (CSP) methods provide the depth to water bottom, and when sufficient signal penetration can be achieved, delineate the depth to bedrock and subbottom materials; (2) continuous resistivity profiling (CRP) methods were used to define the electrical properties of the shallow subbottom, and to possibly determine the distribution of conductive materials, such as clay, and resistive materials, such as sand and bedrock; (3) and magnetometer data were used to identify conductive anomalies of anthropogenic sources, such as cables and metallic debris. All data points were located using global positioning systems (GPS), and the GPS data were used for real-time navigation. The results of the CRP, CSP, and magnetometer data are consistent with the conceptual site model of a bedrock channel incised beneath the present day harbor. The channel appears to follow a north-northwest to south-southeast trend and is parallel to the Pequannock River. The seismic record and boring data indicate that under the channel, the depth to bedrock is as much as 42.7 meters (m) below mean low-low water (MLLW) in the dredged part of the harbor. The bedrock channel becomes shallower towards the shore, where bedrock outcrops have been mapped at land surface. CSP and CRP data were able to provide a discontinuous, but reasonable, trace from the channel toward the west under the proposed southwestern CAD cell. The data indicate a high amount of relief on the bedrock surface, as well as along the water bottom. Under the southwestern CAD cell, the sediments are only marginally thick enough for a CAD cell, at about 8 to 15 m in depth. Some of the profiles show small diffractions in the unconsolidated sediments, but no large-scale boulders or boulder fields were identified. No bedrock reflectors were imaged under the southeastern CAD cell, where core logs indicate the rock is as much as 30 m below MLLW. The chirp frequency, tuned transducer, and boomer-plate CSP surveys were adversely affected by a highly reflective water bottom causing strong multiples in the seismic record and very limited depths of penetration. These multiples are attributed to entrapped gas (methane) in the sediments or to very hard bottom conditions. In a limited number of places, the bedrock surface was observed in the CSP record, creating a discontinuous and sporadic image of the bedrock surface. These interpretations generally matched core data at FP-03-10 and FB-06-1. Use of two analog CSP systems, the boomer plate and tuned transducer, did not overcome the reflections off the water bottom and did not improve the depth of penetration. In general, the CRP profiles were used to corroborate the results of the CSP profiles. Relatively resistive zones associated with the locations of seismic reflections were interpreted as bedrock. The shape of the bedrock surface generally was similar in the CRP and CSP profiles. Evaluation of the CRP profiles indicated that the inversions were adversely affected where the depth and (or) ionic concentration of the water column varied. Consequently, the CRP profiles were broken into short intervals that extended just over the area of interest, where the depth to water bottom was fairly constant. Over these short profiles, efforts were made to evaluate the resistivity of the very shallow sediments to determine if there were any large contrasts in the resistivity of the sediments that might indicate differences in the shallow subbottom materials. No conclusions abo

Ground-penetrating radar--A tool for mapping reservoirs and lakes

USGS Publications Warehouse

Truman, C.C.; Asmussen, L.E.; Allison, H.D.

1991-01-01

Ground-penetrating radar was evaluated as a tool for mapping reservoir and lake bottoms and providing stage-storage information. An impulse radar was used on a 1.4-ha (3.5-acre) reservoir with 31 transects located 6.1 m (20 feet) apart. Depth of water and lateral extent of the lake bottom were accurately measured by ground-penetrating radar. A linear (positive) relationship existed between measured water depth and ground-penetrating radar-determined water depth (R2=0.989). Ground-penetrating radar data were used to create a contour map of the lake bottom. Relationships between water (contour) elevation and water surface area and volume were established. Ground-penetrating radar proved to be a useful tool for mapping lakes, detecting lake bottom variations, locating old stream channels, and determining water depths. The technology provides accurate, continuous profile data in a relatively short time compared to traditional surveying and depth-sounding techniques.

Oxidation of ammonia and methane in an alkaline, saline lake

USGS Publications Warehouse

Joye, S.B.; Connell, T.L.; Miller, L.G.; Oremland, R.S.; Jellison, R.S.

1999-01-01

The oxidation of ammonia (NH3) and methane (CH4) was investigated in an alkaline saline lake, Mono Lake, California (U.S.A.). Ammonia oxidation was examined in April and July 1995 by comparing dark 14CO2 fixation rates in the presence or absence of methyl fluoride (MeF), an inhibitor of NH3 oxidation. Ammonia oxidizer-mediated dark 14CO2 fixation rates were similar in surface (5-7 m) and oxycline (11-15 m) waters, ranging between 70-340 and 89-186 nM d-1, respectively, or 1-7% of primary production by phytoplankton. Ammonia oxidation rates ranged between 580-2,830 nM d-1 in surface waters and 732-1,548 nM d-1 in oxycline waters. Methane oxidation was examined using a 14CH4 tracer technique in July 1994, April 1995, and July 1995. Methane oxidation rates were consistently higher in July, and rates in oxycline and anaerobic bottom waters (0.5-37 and 7-48 nM d-1, respectively) were 10-fold higher than those in aerobic surface waters (0.04-3.8 nM d-1). The majority of CH4 oxidation, in terms of integrated activity, occurred within anoxic bottom waters. Water column oxidation reduced the potential lake-atmosphere CH4 flux by a factor of two to three. Measured oxidation rates and water column concentrations were used to estimate the biological turnover times of NH3 and CH4. The NH3 pool turns over rapidly, on time scales of 0.8 d in surface waters and 10 d within the oxycline, while CH4 is cycled on 103-d time scales in surface waters and 102-d time scales within oxycline and bottom waters. Our data suggest an important role for NH3 oxidation in alkaline, saline lakes since the process converts volatile NH3 to soluble NO2-, thereby reducing loss via lake-atmosphere exchange and maintaining nitrogen in a form that is readily available to phytoplankton.

Dissolved and colloidal trace elements in the Mississippi River Delta outflow after Hurricanes Katrina and Rita

USGS Publications Warehouse

Shim, Moo-Joon; Swarzenski, Peter W.; Shiller, Alan M.

2012-01-01

The Mississippi River delta outflow region is periodically disturbed by tropical weather systems including major hurricanes, which can terminate seasonal bottom water hypoxia and cause the resuspension of shelf bottom sediments which could result in the injection of trace elements into the water column. In the summer of 2005, Hurricanes Katrina and Rita passed over the Louisiana Shelf within a month of each other. Three weeks after Rita, we collected water samples in the Mississippi River delta outflow, examining the distributions of trace elements to study the effect of Hurricanes Katrina and Rita. We observed limited stratification on the shelf and bottom waters that were no longer hypoxic. This resulted, for instance, in bottom water dissolved Mn being lower than is typically observed during hypoxia, but with concentrations still compatible with Mn–O2 trends previously reported. Interestingly, for no element were we able to identify an obvious effect of sediment resuspension on its distribution. In general, elemental distributions were compatible with previous observations in the Mississippi outflow system. Co and Re, which have not been reported for this system previously, showed behavior consistent with other systems: input for Co likely from desorption and conservative mixing for Re. For Cs, an element for which there is little information regarding its estuarine behavior, conservative mixing was also observed. Our filtration method, which allowed us to distinguish the dissolved (<0.02 μm) from colloidal (0.02–0.45 μm) phase, revealed significant colloidal fractions for Fe and Zn, only. For Fe, the colloidal phase was the dominant fraction and was rapidly removed at low salinity. Dissolved Fe, in contrast, persisted out to mid-salinities, being removed in a similar fashion to nitrate. This ability to distinguish the smaller Fe (likely dominantly organically complexed) from larger colloidal suspensates may be useful in better interpreting the bioavailablity of the Fe in estuarine systems.

Characterization of bottom sediments in the Río de la Plata estuary

NASA Astrophysics Data System (ADS)

Simionato, Claudia G.; Moreira, Diego

2016-04-01

Bottom sediments and surface water samples were collected in the intermediate and outer Río de la Plata Estuary during 2009-2010, in six repeated cruises, with 26 stations each. Samples were processed for grain size using a laser particle size analyzer, and water and organic matter contents. The aim of this work is to analyze this data set to provide a comprehensive and objective characterization of the bottom sediments distribution, to study their composition and to progress in the construction of a conceptual model of the involved physical mechanisms. Principal Components Analysis is applied to the bottom sediments size histograms to investigate the spatial patterns. Variations in grain-size parameters contain information on possible sediment transport patterns, which were analyzed by means of trend vectors. Sediments show a gradational arrangement of textures, sand dominant at the head, silt in the intermediate estuary and clayey silt and clay at its mouth; textures become progressively more poorly sorted offshore, and the water and organic matter contents increase. And seem to be strongly related to the geometry and the hydrodynamics. Along the Northern coast of the intermediate estuary, well sorted medium and fine silt predominates, whereas in the Southern coast, coarser and less sorted silt prevails, due to differences in tidal currents and/or in water pathways. Around Barra del Indio, clay prevails over silt and sand, and the water and organic matter contents reach a maximum, probably due flocculation, and the reduction of the currents. Immediately seawards the salt wedge, net transport reverses its direction and well sorted coarser sand from the adjacent shelf dominates. Relict sediment is observed around the Santa Lucía River, consisting of poorly sorted fine silt and clay. The inferred net transport suggests convergence at the Barra del Indio shoal, which is consistent with the constant growing of the banks.

Dissolved and colloidal trace elements in the Mississippi River delta outflow after Hurricanes Katrina and Rita

NASA Astrophysics Data System (ADS)

Shim, Moo-Joon; Swarzenski, Peter W.; Shiller, Alan M.

2012-07-01

The Mississippi River delta outflow region is periodically disturbed by tropical weather systems including major hurricanes, which can terminate seasonal bottom water hypoxia and cause the resuspension of shelf bottom sediments which could result in the injection of trace elements into the water column. In the summer of 2005, Hurricanes Katrina and Rita passed over the Louisiana Shelf within a month of each other. Three weeks after Rita, we collected water samples in the Mississippi River delta outflow, examining the distributions of trace elements to study the effect of Hurricanes Katrina and Rita. We observed limited stratification on the shelf and bottom waters that were no longer hypoxic. This resulted, for instance, in bottom water dissolved Mn being lower than is typically observed during hypoxia, but with concentrations still compatible with Mn-O2 trends previously reported. Interestingly, for no element were we able to identify an obvious effect of sediment resuspension on its distribution. In general, elemental distributions were compatible with previous observations in the Mississippi outflow system. Co and Re, which have not been reported for this system previously, showed behavior consistent with other systems: input for Co likely from desorption and conservative mixing for Re. For Cs, an element for which there is little information regarding its estuarine behavior, conservative mixing was also observed. Our filtration method, which allowed us to distinguish the dissolved (<0.02 μm) from colloidal (0.02-0.45 μm) phase, revealed significant colloidal fractions for Fe and Zn, only. For Fe, the colloidal phase was the dominant fraction and was rapidly removed at low salinity. Dissolved Fe, in contrast, persisted out to mid-salinities, being removed in a similar fashion to nitrate. This ability to distinguish the smaller Fe (likely dominantly organically complexed) from larger colloidal suspensates may be useful in better interpreting the bioavailablity of the Fe in estuarine systems.

Seasonality of bottom water temperature in the northern North Sea reconstructed from the oxygen isotope composition of the bivalve Arctica islandica

NASA Astrophysics Data System (ADS)

Trofimova, Tamara; Andersson, Carin; Bonitz, Fabian

2017-04-01

The seasonality of temperature changes is an important characteristic of climate. However, observational data for the ocean are only available for the last 150 year from a limited number of locations. Prior to 18th century information is only available from proxy reconstructions. The vast majority of such reconstructions depend on land-based archives, primarily from dendrochronology. Established marine proxy records for the ocean, especially at high latitudes, are both sparsely distributed and poorly resolved in time. Therefore, the identification and development of proxies for studying key ocean processes at sub-annual resolution that can extend the marine instrumental record is a clear priority in marine climate science. In this study, we have developed a record of early Holocene seasonal variability of bottom water temperature from the Viking Bank in the northern most North Sea. This area is of a particular interest since the hydrography is controlled by the inflow of Atlantic water. The reconstruction is based on the oxygen isotope composition of the growth increments in two sub-fossil shells of Arctica islandica (Bivalvia), dated to 9600-9335 cal. yr BP. By combining radiocarbon dating and sclerochronological techniques a floating chronology spanning over 200 years was constructed. Using the chronology as an age model, oxygen isotope measurements from 2 shells were combined into a 22-years long record. The results from this oxygen isotope record are compared with stable oxygen isotope profiles from modern shells to estimate changes in the mean state and seasonality between present and early Holocene. Shell-derived oxygen isotope values together with ice-volume corrected oxygen isotope values for the seawater were used to calculate bottom-water temperatures on a sub-annual time-scale. Preliminary results of the reconstructed early Holocene bottom water temperature indicate higher seasonality and lower minimum temperature compared to the present.

Orbital and suborbital variability in North Atlantic bottom water temperature obtained from deep-sea ostracod Mg/Ca ratios

USGS Publications Warehouse

Cronin, T. M.; Dwyer, G.S.; Baker, P.A.; Rodriguez-Lazaro, J.; DeMartino, D.M.

2000-01-01

Magnesium/calcium (Mg/Ca) ratios were measured in the deep-sea ostracod (Crustacea) genus Krithe from Chain core 82-24-4PC from the western mid-Atlantic Ridge (3427 m) in order to estimate ocean circulation and bottom water temperature (BWT) variability over the past 200,000 years. Mg/Ca ratios have been used as a paleothermometer because the ratios are controlled primarily by ambient water temperatures at the time the organism secretes its adult carapace. Over the past two glacial–interglacial cycles, Mg/Ca values oscillated between about 7 mmol/mol and 12 mmol/mol, equivalent to a BWT range of 0 to >3.5°C. The lowest values were obtained on specimens from glacial marine isotope stages (MISs) 2, 4 and 6; the highest values were obtained from specimens from the early part of the Holocene interglacial (MIS 1), and also from MISs 5 and 7. These trends suggest that BWTs in the North Atlantic Ocean fluctuate over orbital time scales.Suborbital variability in Mg/Ca ratios and BWT was also observed for the past 100,000 years. Ratios rose from ∼8 mmol/mol to ∼10 mmol/mol (implying a BWT increase of ∼1 to 3°C) during 14 Mg/Ca excursions. The highest ratios were found in Krithe dated at approximately 32, 36–38, 43, 48, 73, 85 and 93 ka. Although the age model for the Chain 82-24-4PC and temporal resolution do not allow precise correlation, some of these deep-sea bottom temperature excursions appear to correspond to Heinrich events recorded in other regions of the North Atlantic and perhaps Dansgaard–Oeschger interstadial events recorded in Greenland ice cores. If confirmed, this would support the hypothesis that millennial-scale oscillations of climate in the North Atlantic are capable of affecting global climate via thermohaline circulation changes.

Analyses of water, bank material, bottom material, and elutriate samples collected near Belzoni, Mississippi (upper Yazoo projects)

USGS Publications Warehouse

Brightbill, David B.; Treadway, Joseph B.

1980-01-01

Four core-material-sampling sites and one bottom-material site were chosen by the U.S. Army Corps of Engineers to represent areas of proposed dredging activity along a 24.9-mile reach of the upper Yazoo River. Five receiving-water sites also were selected to represent the water that will contact the proposed dredged material. Chemical and physical analyses were performed upon core or bottom material and native-water (receiving-water) samples from these sites as well as upon elutriate samples of the mixture of sediment and receiving water. The results of these analyses are presented without interpertation. (USGS)

Borehole sounding device with sealed depth and water level sensors

DOEpatents

Skalski, Joseph C.; Henke, Michael D.

2005-08-02

A borehole device having proximal and distal ends comprises an enclosure at the proximal end for accepting an aircraft cable containing a plurality of insulated conductors from a remote position. A water sensing enclosure is sealingly attached to the enclosure and contains means for detecting water, and sending a signal on the cable to the remote position indicating water has been detected. A bottom sensing enclosure is sealingly attached to the water sensing enclosure for determining when the borehole device encounters borehole bottom and sends a signal on the cable to the remote position indicating that borehole bottom has been encountered.

Observed bottom boundary layer transport and uplift on the continental shelf adjacent to a western boundary current

NASA Astrophysics Data System (ADS)

Schaeffer, A.; Roughan, M.; Wood, J. E.

2014-08-01

Western boundary currents strongly influence the dynamics on the adjacent continental shelf and in particular the cross-shelf transport and uplift through the bottom boundary layer. Four years of moored in situ observations on the narrow southeastern Australian shelf (in water depths of between 65 and 140 m) were used to investigate bottom cross-shelf transport, both upstream (30°S) and downstream (34°S) of the separation zone of the East Australian Current (EAC). Bottom transport was estimated and assessed against Ekman theory, showing consistent results for a number of different formulations of the boundary layer thickness. Net bottom cross-shelf transport was onshore at all locations. Ekman theory indicates that up to 64% of the transport variability is driven by the along-shelf bottom stress. Onshore transport in the bottom boundary layer was more intense and frequent upstream than downstream, occurring 64% of the time at 30°S. Wind-driven surface Ekman transport estimates did not balance the bottom cross-shelf flow. At both locations, strong variability was found in bottom water transport at periods of approximately 90-100 days. This corresponds with periodicity in EAC fluctuations and eddy shedding as evidenced from altimeter observations, highlighting the EAC as a driver of variability in the continental shelf waters. Ocean glider and HF radar observations were used to identify the bio-physical response to an EAC encroachment event, resulting in a strong onshore bottom flow, the uplift of cold slope water, and elevated coastal chlorophyll concentrations.

Early transformation of the Mediterranean Outflow Water (MOW) in the Gulf Of Cádiz, SW Iberian Peninsula: pathways, mixing and temporal variability.

NASA Astrophysics Data System (ADS)

Sánchez Leal, Ricardo F.; Sánchez Garrido, José Carlos; Jesús Bellanco Esteban, María; Ruiz Villarreal, Manuel; González-Pola Muñiz, César

2014-05-01

The inverse estuarine circulation through the strait of Gibraltar is responsible for the overflow of dense, saline MOW towards the Atlantic basin. Initially as a gravity undercurrent, the MOW entrains large amounts of the overlying Eastern North Atlantic Central Water to become a multi-layered, buoyant plume at depths of 800-1300 m past Cape St. Vincent. Much of the entrainment occurs within 100 km of the Strait over a highly abrupt topography. In this work we analyze a repeated series of high-resolution CTD-LADCP observations along a number of standard sections crossing the early MOW. These data show that from the Strait of Gibraltar, the bottom-trapped flow bifurcates in the vicinity of the topographic features, diverting or rejoining the main MOW path as a function of the orientation of channels and valleys. As it turns anticyclonically, the undercurrent exhibits a cross-axis geostrophic gradient, with the margin closer to the slope being in near-geostrophic balance whereas the distal band is largely ageostrophic due to the flow curvature. Mixing is steered by the interplay of tidal stirring, bottom roughness, shear instability and double diffusion along the MOW path. Data also shows that seasonal variability is mostly related to the fluctuations in the overlying layer rather than to MOW dynamics. This is a contribution to INGRES3 project (Mediterranean outflow at Gibraltar, its influence on deep Mediterranean water ventilation and first transformation and coupling with North-Atlantic central waters in the Gulf of Cádiz, CTM2010_21229)

Sulfide as a Chemoautotrophic Electron Donor for Dissimilatory Arsenate Reduction in Mono Lake, California

NASA Astrophysics Data System (ADS)

Hoeft, S. E.; Kulp, T. R.; Stolz, J. S.; Oremland, R. S.

2003-12-01

In aqueous systems, arsenic occurs as arsenate [As(V)] or as arsenite [As(III)], with the latter form being more toxic and mobile. Mono Lake, California is a meromictic soda lake (pH = 9.8; salinity = 70-90 g/L) with exceptionally high arsenic content ( ˜200 μ M), a consequence of hydrothermal inputs combined with evaporative concentration. Previous work has shown that arsenic speciation changes from As(V) to the more reduced As(III) with vertical transition from the lake's surface oxic waters to its unmixed, anoxic bottom waters and that dissimilatory reduction is responsible for the observed change in arsenic speciation. Rates of in situ dissimilatory As(V) reduction measured by radiotracer ( ˜1- 6 μ mol/L/d) were estimated to be significant enough to mineralize up to 14% of annual primary productivity. Subsequent lab-based investigations with As(V)-amended ( ˜1-2 mM) bottom water displayed significantly higher rates (150-260 μ mol/L/d) of As(V) reduction and were not limited by the availability of organic electron donors such as acetate, lactate, malate and glucose. The focus of this study was to identify a natural source of electrons for As(V) reduction in Mono Lake. While Mono Lake contains plentiful dissolved organic carbon ( ˜7 mM) this material is usually refractory and resistant to bacterial oxidation. Alternatively, the anoxic bottom waters contain high concentrations of sulfide ions ( ˜1-2 mM) that could potentially serve as an electron donor for dissimilatory As(V) reduction. In a time course experiment with As(V)-amended Mono Lake bottom water, we observed oxidation of sulfide linked to the reduction of As(V) to As(III). This reaction did not occur in filter sterilized controls and sulfide loss did not occur in samples lacking As(V). In bottom water amended with additional sulfide (total = 6 mM) and As(V), we observed a linear relationship between rates of dissimilatory As(V) reduction and As(V) concentration. The highest rate observed under these conditions was ˜3 mmol/L/d, over 1000-fold higher than Mono Lake in situ rates. We isolated an anaerobic bacterium from Mono Lake bottom water, strain MLMS-1, that grows in mineral salts media by oxidizing sulfide to sulfate and reducing As(V) to As(III). MLMS-1 grew with a 4:1 stoichiometry of As(V) reduced to sulfide oxidized, indicating an 8 electron transfer. MLMS-1 aligned by 16S rDNA amplification and sequencing in the δ -Proteobacteria, being closely related to the sulfate-reducing bacteria of the genus Desulfobulbus. However, strain MLMS-1 does not grow with sulfate as an electron acceptor.

A modern vs. Permian black shale - the hydrography, primary productivity, and water-column chemistry of deposition

USGS Publications Warehouse

Piper, D.Z.; Perkins, R.B.

2004-01-01

The sediment currently accumulating in the Cariaco Basin, on the continental shelf of Venezuela, has an elevated organic-carbon content of approximately 5%; is accumulating under O2-depleted bottom-water conditions (SO42- reduction); is composed dominantly of foraminiferal calcite, diatomaceous silica, clay, and silt; and is dark greenish gray in color. Upon lithification, it will become a black shale. Recent studies have established the hydrography of the basin and the level of primary productivity and bottom-water redox conditions. These properties are used to model accumulation rates of Cd, Cr, Cu, Mo, Ni, V, and Zn on the seafloor. The model rates agree closely with measured rates for the uppermost surface sediment.The model is applied to the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, a phosphate deposit of Permian age in the northwest United States. It too has all of the requisite properties of a black shale. Although the deposit is a world-class phosphorite, it is composed mostly of phosphatic mudstone and siltstone, chert, limestone, and dolomite. It has organic-carbon concentrations of up to 15%, is strongly enriched in several trace elements above a terrigenous contribution and is black. The trace-element accumulation defines a mean primary productivity in the photic zone of the Phosphoria Basin as moderate, at 500 g m-2 year-1 organic carbon, comparable to primary productivity in the Cariaco Basin. The source of nutrient-enriched water that was imported into the Phosphoria Basin, upwelled into the photic zone, and supported primary productivity was an O2 minimum zone of the open ocean. The depth range over which the water was imported would have been between approximately 100 and 600 m. The mean residence time of bottom water in the basin was approximately 4 years vs. 100 years in the Cariaco Basin. The bottom water was O2 depleted, but it was denitrifying, or NO3- reducing, rather than SO42- reducing. Published by Elsevier B.V.

A three dimensional Dirichlet-to-Neumann map for surface waves over topography

NASA Astrophysics Data System (ADS)

Nachbin, Andre; Andrade, David

2016-11-01

We consider three dimensional surface water waves in the potential theory regime. The bottom topography can have a quite general profile. In the case of linear waves the Dirichlet-to-Neumann operator is formulated in a matrix decomposition form. Computational simulations illustrate the performance of the method. Two dimensional periodic bottom variations are considered in both the Bragg resonance regime as well as the rapidly varying (homogenized) regime. In the three-dimensional case we use the Luneburg lens-shaped submerged mound, which promotes the focusing of the underlying rays. FAPERJ Cientistas do Nosso Estado Grant 102917/2011 and ANP/PRH-32.

Interdecadal changes in intensity of the oxygen minimum zone off Concepción, Chile (~ 36° S), over the last century

NASA Astrophysics Data System (ADS)

Srain, B.; Pantoja, S.; Sepúlveda, J.; Lange, C. B.; Muñoz, P.; Summons, R. E.; McKay, J.; Salamanca, M.

2015-10-01

We reconstructed oxygenation changes in the upwelling ecosystem off Concepción (36° S), Chile, using inorganic and organic proxies in a sediment core covering the last ca. 110 years of sedimentation in this area. Authigenic enrichments of Mo, U and Cd were observed between ca. 1935 and 1971 CE, implying a prolonged period with predominantly more reduced conditions in bottom waters and surface sediments. Significant positive correlations between redox-sensitive metals, algal sterols, biomarkers of micro-aerophilic and anaerobic microorganisms, and archaeal glycerol dialkyl glycerol tetraethers point to a tight coupling among bottom water O2 depletion and increased primary and export production. The time interval with low O2 of ca. 35 years seems to follow low-frequency interdecadal variation of the Pacific Decadal Oscillation, and it may have resulted in O2 depletion over the entire continental shelf off Concepción. Taking this together with the concurrent increase in sedimentary molecular indicators of micro-aerophilic and anaerobic microbes, we can suggest that changes in oxygenation of the water column are reflected by changes in microbial community. This study can inform our understanding of ecological consequences to projected trends in ocean deoxygenation.

Fluxes of dissolved methane from the seafloor at the landward limit of the gas hydrate stability zone offshore western Svalbard

NASA Astrophysics Data System (ADS)

Graves, Carolyn; Steinle, Lea; Niemann, Helge; Rehder, Gregor; Fisher, Rebecca; Lowry, Dave; Connelly, Doug; James, Rachael

2015-04-01

Seepage of methane from seafloor sediments offshore Svalbard may partly be driven by destabilization of gas hydrates as a result of bottom water warming. As the world's oceans are expected to continue to warm, in particular in the Arctic, destabilization of hydrate may become an important source of methane to ocean bottom waters and potentially to the overlying atmosphere where it contributes to further warming. In order to quantify the fate of methane from seafloor seeps, we have determined the distribution of dissolved methane in the water column on the upper slope and shelf offshore western Svalbard during three research cruises with RRS James Clark Ross (JR253) in 2011 and R/V Maria S. Merian (MSM21/4) and Heincke (HE387) in 2012. Combining discrete depth profile methane concentration data and surface seawater concentrations from an equilibrator-online system with oxidation rate measurements and atmospheric methane observations allows insight into the fate of methane input from the seafloor, and evaluation of the potential contributions of other methane sources. A simple box model considering oxidation and horizontal and vertical mixing indicates that the majority of seep methane is oxidized at depth. A plume of high methane concentrations is expected to persist more than 100 km downstream of the seepage area in the rapid barotropic West Spitsbergen Current, which flows northward towards the Arctic Ocean. We calculate that the diffusive sea-air flux of methane is largest on the shallow shelf, reaching 36 μmol m-2 day-1. Over the entire western Svalbard region there is a persistent, but small, source of methane from surface seawater to the overlying atmosphere. Measurements of the atmospheric methane carbon isotope signature indicate that the seafloor seeps do not make a significant contribution to atmospheric methane in this region, which is consistent with earlier studies. Observations downstream of the seepage region are necessary to further constrain potential for transport of previously hydrate-bound methane to the atmosphere, which would require a mechanism for enhanced vertical mixing of dissolved methane from bottom waters into the surface mixed layer.

Non-local rheology of stony debris flow propagating over a cohesionless sediment bed

NASA Astrophysics Data System (ADS)

Lanzoni, Stefano; Gregoretti, Carlo

2016-04-01

Velocity profiles of gravel-water mixtures observed in flume experiments often exhibit a double-slope behavior, with a lower narrower region where the velocity increases slowly, and an upper wider region often exhibiting a nearly linear behavior. Even though the flow can be classified within the grain-inertia regime, the overall profile seems to not conform to the power law (with exponent 1.5) distribution obtained by integrating along the normal to the flow the dispersive stresses envisaged by Bagnold (1954) in his pioneer work. Note that this formulation neglects the contribution to the velocity profile of the quasi-static (frictional) stresses that tend to dominate close to an erodible sediment bottom. The present work investigates the possibility to find out a uniformly valid distribution of shear stress from the bottom to the flow surface. To this aim we follow a heuristic coherence length approach (GDR-MIDI, 2004) similar to the mixing length procedure commonly used to study the atmospheric boundary layer over canopy (see, e.g., Harmann and Finnegan, 2007). A database built on 64 systematic debris flow experiments is used to disclose the general features of velocity profiles that establish within the body of almost steady water-sediment flows and the dependence of transport sediment volumetric concentration on the relevant parameters. The almost steady water-sediment flows considered in the study were generated by releasing a prescribed water discharge on a saturated layer of sediment (specifically, 3 mm gravel, 6 mm gravel, and 3 mm glass spheres) initially placed in a 10 m long and 0.2 m wide laboratory flume. The analysis clearly indicates that stony debris flow conditions characterized the experiments. The mixing length does not result constant, as required by a Bagnold-like profile, but varies gradually, from zero at the flow surface, to a finite value near the erodible bottom. We discuss this structure in terms of shear stress distribution along the normal to the flow, with particular attention to the role played by frictional stresses near to the movable bed over which the debris flow propagates.

Current status of emerging hypoxia in a eutrophic estuary: The lower reach of the Pearl River Estuary, China

NASA Astrophysics Data System (ADS)

Qian, Wei; Gan, Jianping; Liu, Jinwen; He, Biyan; Lu, Zhongming; Guo, Xianghui; Wang, Deli; Guo, Liguo; Huang, Tao; Dai, Minhan

2018-05-01

We examine the current status of dissolved oxygen (DO) and its trend over the past 25 years in the lower Pearl River Estuary, a large eutrophic estuary located in Southern China and surrounded by large cities including Hong Kong, Shenzhen and Guangzhou. Monthly cruises conducted from April 2010 to March 2011 clearly show that DO depletion began to emerge in the bottom layer of the lower estuary off Hong Kong in June, and became fully developed in July and August when oxygen-deficient water occupied ∼1000 km2 before gradually becoming re-oxygenated in September and October. The development of the low oxygen zone was closely coupled with phytoplankton blooms in the surface water, which was supersaturated with respect to DO suggesting the importance of autochthonous organic matter in fueling bottom DO consumption after settling through the pycnocline. Long-term monitoring data collected in the study area adjacent to Hong Kong by the Hong Kong Environmental Protection Department showed a decreasing trend of ∼2 ± 0.9 μmol kg-1 yr-1 in the annual minimum DO concentration in bottom water over the past 25 years. Associated with the decrease in DO was an increase in the annual maximum surface concentration of dissolved inorganic nitrogen (DIN) at a rate of ∼1.4 ± 0.3 μmol kg-1 yr-1, suggesting again that eutrophication is the most plausible driver of oxygen deficiency in this region. Therefore, our monthly cruises, along with the decadal monitoring data, reveal a large low oxygen zone, likely developing into a large hypoxic zone driven primarily by anthropogenic eutrophication. This new development suggests environmental stressors such as eutrophication may have a cascading effect, with important and expensive consequences for the regional environment.

May 1984-Aril 1985 Water Budget of Reelfoot Lake With Estimates of Sediment Inflow and Concentrations of Pesticides in Bottom Material in Tributary Streams--Basic Data Report

DTIC Science & Technology

1985-01-01

Open-File Report 85-498 MAY 1984-APRIL 1985 WATER BUDGET OF REELFOOT LAKE WITH ESTIMATES OF SEDIMENT INFLOW AND CONCENTRATIONS OF PESTICIDES IN...AND SUBTITLE May 1984-Apr 1985 Water Budget of Reelfoot Lake With Estimates of Sediment Inflow and Concentrations of Pesticides in Bottom Material in...1984-APRIL 1985 WATER BUDGET OF REELFOOT LAKE WITH ESTIMATES OF SEDIMENT INFLOW AND CONCENTRATIONS OF PESTICIDES IN BOTTOM MATERIAL IN TRIBUTARY

Paleoenvironmental History of Long Island Sound, CT, USA

NASA Astrophysics Data System (ADS)

Varekamp, J. C.; Thomas, E.; Lugolobi, F.; Buchholtz Ten Brink, M. R.

2002-12-01

Western Long Island Sound (LIS) is an urban estuary heavily impacted by waste water effluents from CT and New York city. The estuary has suffered seasonal hypoxia since the 1970s, and in 1999 lobsters suffered > 90% mortality. We used short sediment cores that cover the last several 100 years to reconstruct the temperature/salinity history of LIS, as well as its history of hypoxic episodes. We measured oxygen and carbon isotopic compositions and Mg/Ca and Sr/Ca in calcite tests of the benthic foraminifer Elphidium excavatum, collected alive (Rose Bengal stained) in grab samples and in core samples, as proxies for bottom water temperature and salinity. The level of bottom water oxygenation is derived from the carbon isotope values in foraminiferal calcite, after correction for paleosalinity. The strong seasonal temperature fluctuation in Long Island Sound bottom waters (about 20oC) and the long livespan of the foraminifer make precise paleotemperature estimates difficult. The oxygen isotope data (in vivo effect 1.1 o/_{oo} of the foraminiferal tests were recalculated at constant mean-annual water temperature (12.5^{o}C) into paleosalinities, ranging between 18 and 33 ^{o}/oo. The oxygen and carbon isotope ratios of river water, Long Island Sound water and dissolved inorganic carbon were used to construct a mixing model for the Sound. From calculated paleosalinities and the modern mixing model we derived expected carbon isotope ratios, which were subtracted from the observed values. We argue that the residuals (excess carbon isotope values) are proportional to the amount of organic carbon that was oxidized in these waters, and as such represent a proxy for paleohypoxia. Data from nine cores show no long term trends in salinity over the last 1000 years, but show more pronounced variations over the last 100 years. Several low salinity events could be correlated with wet climate periods documented in Southern New England. The excess carbon isotope values were between 0 and -1 o/_{oo} for most of the last millennium but became much more negative in the mid 18^{th} to 19^{th} century, with strong variability in the 20^{th} century. The low salinity events of the last 100 years correlate strongly with strongly negative excess carbon isotope values, suggesting a linkage between the wet periods and oxidation of organic matter on the bottom of the Sound (algal blooms, warm periods?). This linkage between low salinity events and strongly negative excess carbon isotope values did not occur prior to 1900 AD. More detailed dating (^{210}Pb, ^{137}$Cs) will improve the time resolution and correlation between cores of the various documented events.

Treated bottom ash medium and method of arsenic removal from drinking water

DOEpatents

Gadgil, Ashok

2009-06-09

A method for low-cost arsenic removal from drinking water using chemically prepared bottom ash pre-treated with ferrous sulfate and then sodium hydroxide. Deposits on the surface of particles of bottom ash form of activated iron adsorbent with a high affinity for arsenic. In laboratory tests, a miniscule 5 grams of pre-treated bottom ash was sufficient to remove the arsenic from 2 liters of 2400 ppb (parts per billion) arsenic-laden water to a level below 50 ppb (the present United States Environmental Protection Agency limit). By increasing the amount of pre-treated bottom ash, even lower levels of post-treatment arsenic are expected. It is further expected that this invention supplies a very low-cost solution to arsenic poisoning for large population segments.

Experimental observation of standing interfacial waves induced by surface waves in muddy water

NASA Astrophysics Data System (ADS)

Maxeiner, Eric; Dalrymple, Robert A.

2011-09-01

A striking feature has been observed in a laboratory wave tank with a thin layer of clear water overlying a layer of mud. A piston-type wave maker is used to generate long monochromatic surface waves in a tank with a layer of kaolinite clay at the bottom. The wave action on the mud causes the clay particles to rise from the bottom into the water column, forming a lutocline. As the lutocline approaches the water surface, a set of standing interfacial waves form on the lutocline. The interfacial wave directions are oriented nearly orthogonal to the surface wave direction. The interfacial waves, which sometimes cover the entire length and width of the tank, are also temporally subharmonic as the phase of the interfacial wave alternates with each passing surface wave crest. These interfacial waves are the result of a resonant three-wave interaction involving the surface wave train and the two interfacial wave trains. The interfacial waves are only present when the lutocline is about 3 cm of the water surface and they can be sufficiently nonlinear as to exhibit superharmonics and a breaking-type of instability.

El Cobreloa: A geyser with two distinct eruption styles

NASA Astrophysics Data System (ADS)

Namiki, A.; Munoz, C.; Manga, M.; Hurwitz, S.; King, E.; Negri, A.; Ortega, P.; Patel, A.; Rudolph, M.

2013-12-01

El Cobreloa geyser has two distinct eruption styles: vigorous major eruptions, and less energetic minor eruptions. Minor eruptions splash hot water intermittently over an approximately 4 minute time period. Major eruptions begin with an eruption style similar to minor eruptions, but then transition to a voluminous and water-dominated eruption, and finally end with energetic steam discharge. The steam discharge continues for approximately 1 hour. We calculated the eruption intervals by visual observations, acoustic measurements, and ground temperature measurements. All of measurements consistently show that each eruption style has a regular interval: 4 hours and 40 minutes for major eruptions, and ~13 minutes for minor eruptions. From these observations, we infer that there are two boiling loci that source each type of eruption, one at the bottom and the other at the top of the conduit. If the bottom of the conduit is hot enough, boiling begins at the bottom of the conduit to make a steam slug. As this slug ascends in the conduit, it heats the surrounding water. If the slug rises fast enough it splashes water when it reaches the surface, creating minor eruptions. Each successive steam slug continues to heat water in the conduit until it eventually reaches the boiling temperature everywhere. Once the top of the conduit begins boiling, the energetic steam discharge begins and the boiling propagates downward. Such a process causes major eruption. Geysers are often studied as an analogue to magmatic volcanoes because it is easier to document how mass and energy transfer lead to eruptions. El Cobreloa provides insight into how the system becomes primed for large eruptions.

4SM: A Novel Self-Calibrated Algebraic Ratio Method for Satellite-Derived Bathymetry and Water Column Correction

PubMed Central

Morel, Yann G.; Favoretto, Fabio

2017-01-01

All empirical water column correction methods have consistently been reported to require existing depth sounding data for the purpose of calibrating a simple depth retrieval model; they yield poor results over very bright or very dark bottoms. In contrast, we set out to (i) use only the relative radiance data in the image along with published data, and several new assumptions; (ii) in order to specify and operate the simplified radiative transfer equation (RTE); (iii) for the purpose of retrieving both the satellite derived bathymetry (SDB) and the water column corrected spectral reflectance over shallow seabeds. Sea truth regressions show that SDB depths retrieved by the method only need tide correction. Therefore it shall be demonstrated that, under such new assumptions, there is no need for (i) formal atmospheric correction; (ii) conversion of relative radiance into calibrated reflectance; or (iii) existing depth sounding data, to specify the simplified RTE and produce both SDB and spectral water column corrected radiance ready for bottom typing. Moreover, the use of the panchromatic band for that purpose is introduced. Altogether, we named this process the Self-Calibrated Supervised Spectral Shallow-sea Modeler (4SM). This approach requires a trained practitioner, though, to produce its results within hours of downloading the raw image. The ideal raw image should be a “near-nadir” view, exhibit homogeneous atmosphere and water column, include some coverage of optically deep waters and bare land, and lend itself to quality removal of haze, atmospheric adjacency effect, and sun/sky glint. PMID:28754028

4SM: A Novel Self-Calibrated Algebraic Ratio Method for Satellite-Derived Bathymetry and Water Column Correction.

PubMed

Morel, Yann G; Favoretto, Fabio

2017-07-21

All empirical water column correction methods have consistently been reported to require existing depth sounding data for the purpose of calibrating a simple depth retrieval model; they yield poor results over very bright or very dark bottoms. In contrast, we set out to (i) use only the relative radiance data in the image along with published data, and several new assumptions; (ii) in order to specify and operate the simplified radiative transfer equation (RTE); (iii) for the purpose of retrieving both the satellite derived bathymetry (SDB) and the water column corrected spectral reflectance over shallow seabeds. Sea truth regressions show that SDB depths retrieved by the method only need tide correction. Therefore it shall be demonstrated that, under such new assumptions, there is no need for (i) formal atmospheric correction; (ii) conversion of relative radiance into calibrated reflectance; or (iii) existing depth sounding data, to specify the simplified RTE and produce both SDB and spectral water column corrected radiance ready for bottom typing. Moreover, the use of the panchromatic band for that purpose is introduced. Altogether, we named this process the Self-Calibrated Supervised Spectral Shallow-sea Modeler (4SM). This approach requires a trained practitioner, though, to produce its results within hours of downloading the raw image. The ideal raw image should be a "near-nadir" view, exhibit homogeneous atmosphere and water column, include some coverage of optically deep waters and bare land, and lend itself to quality removal of haze, atmospheric adjacency effect, and sun/sky glint.

Stable isotope evidence for the Bottom Convective Layer homogeneity in the Black Sea

PubMed Central

2014-01-01

The Black Sea is the largest euxinic basin on the Earth. The anoxic zone consists of the upper part water mass stratified by density, and the lower water mass homogenized relative to density (depth >1750 m), named the Bottom Convective Layer. To assess homogeneity and possible exchange of matter across the upper and lower boundaries of the Bottom Convective Layer, new data on stable isotope composition of S, O and H were obtained. Samples were collected in August 2008 and March 2009 from two stations located in the eastern central part of the Black Sea. Distribution of δ18O and δD values of water for the entire water column did not vary seasonally. Appreciable differences were marked for δD value variation in the picnocline area (water depth 200-400 m) and in the BCL 5 m above the bottom that might be caused by penetration of intrusions with elevated portion of shelf modified Mediterranean Water. Observed linear relationship between δ18O (or δD) and salinity indicates that mixing water and salt occurs at the same time, and the deep water of the Black Sea has two end members: the high-salinity Mediterranean seawater and freshwater input. In the Bottom Convective Layer, the average δ34S (H2S) was -40.6 ± 0.5‰ and did not vary seasonally. At the bottom (depth > 2000 m), 34S depletion down to –41.0‰ was observed. Our δ34S (SO4) data are by 2-3‰ higher than those measured previously for the Bottom Convective Layer. Sulfate from the aerobic zone with δ34S (SO4) = +21‰ corresponds to ocean water sulfate and that has not been subjected to sulfate reduction. Average δ34S (SO4) values for depths > 1250 m were found to be +23.0 ± 0.2‰ (1σ). Sulfur isotope composition of sulfate does not change in the Bottom Convective Layer and on its upper and lower boundaries, and does not depend on the season of observation. PMID:24739078

Extreme diel dissolved oxygen and carbon cycles in shallow vegetated lakes.

PubMed

Andersen, Mikkel R; Kragh, Theis; Sand-Jensen, Kaj

2017-09-13

A common perception in limnology is that shallow lakes are homogeneously mixed owing to their small water volume. However, this perception is largely gained by downscaling knowledge from large lakes to their smaller counterparts. Here we show that shallow vegetated lakes (less than 0.6 m), in fact, undergo recurring daytime stratification and nocturnal mixing accompanied by extreme chemical variations during summer. Dense submerged vegetation effectively attenuates light and turbulence generating separation between warm surface waters and much colder bottom waters. Photosynthesis in surface waters produces oxygen accumulation and CO 2 depletion, whereas respiration in dark bottom waters causes anoxia and CO 2 accumulation. High daytime pH in surface waters promotes precipitation of CaCO 3 which is re-dissolved in bottom waters. Nocturnal convective mixing re-introduces oxygen into bottom waters for aerobic respiration and regenerated inorganic carbon into surface waters, which supports intense photosynthesis. Our results reconfigure the basic understanding of local environmental gradients in shallow lakes, one of the most abundant freshwater habitats globally. © 2017 The Author(s).

The analysis of bottom forming process for hybrid heating device

NASA Astrophysics Data System (ADS)

Bałon, Paweł; Świątoniowski, Andrzej; Kiełbasa, Bartłomiej

2017-10-01

In this paper the authors present an unusual method for bottom forming applicable for various industrial purposes including the manufacture of water heaters or pressure equipment. This method allows for the fabrication of the bottom of a given piece of stainless steel into a pre-determined shape conforming to the DIN standard which determines the most advantageous dimensions for the bottom cross section in terms of working pressure loading. The authors checked the validity of the method in a numerical and experimental way generating a tool designed to produce bottoms of specified geometry. Many problems are encountered during the design and production of parts, especially excessive sheet wrinkling over a large area of the part. The experiment showed that a lack of experience and numerical analysis in the design of such elements would result in the production of highly wrinkled parts. This defect would render the parts impossible to assemble with the cylindrical part. Many tool shops employ a method for drawing elements with a spherical surface which involves additional spinning, stamping, and grading operations, which greatly increases the cost of parts production. The authors present and compare two forming methods for spherical and parabolic objects, and experimentally confirm the validity of the sheet reversing method with adequate pressure force. The applied method produces parts in one drawing operation and in a following operation that is based on laser or water cutting to obtain a round blank. This reduces the costs of tooling manufacturing by requiring just one tool which can be placed on any hydraulic press with a minimum force of 2 000 kN.

Trends in summer bottom-water temperatures on the northern Gulf of Mexico continental shelf from 1985 to 2015.

PubMed

Turner, R Eugene; Rabalais, Nancy N; Justić, Dubravko

2017-01-01

We quantified trends in the 1985 to 2015 summer bottom-water temperature on the northern Gulf of Mexico (nGOM) continental shelf for data collected at 88 stations with depths ranging from 3 to 63 m. The analysis was supplemented with monthly data collected from 1963 to 1965 in the same area. The seasonal summer peak in average bottom-water temperature varied concurrently with air temperature, but with a 2- to 5-month lag. The summer bottom-water temperature declined gradually with depth from 30 oC at stations closest to the shore, to 20 oC at the offshore edge of the study area, and increased an average 0.051 oC y-1 between1963 and 2015. The bottom-water warming in summer for all stations was 1.9 times faster compared to the rise in local summer air temperatures, and 6.4 times faster than the concurrent increase in annual global ocean sea surface temperatures. The annual rise in average summer bottom-water temperatures on the subtropical nGOM continental shelf is comparable to the few published temperature trend estimates from colder environments. These recent changes in the heat storage on the nGOM continental shelf will affect oxygen and carbon cycling, spatial distribution of fish and shrimp, and overall species diversity.

Evaluation of multi-resolution satellite sensors for assessing water quality and bottom depth of Lake Garda.

PubMed

Giardino, Claudia; Bresciani, Mariano; Cazzaniga, Ilaria; Schenk, Karin; Rieger, Patrizia; Braga, Federica; Matta, Erica; Brando, Vittorio E

2014-12-15

In this study we evaluate the capabilities of three satellite sensors for assessing water composition and bottom depth in Lake Garda, Italy. A consistent physics-based processing chain was applied to Moderate Resolution Imaging Spectroradiometer (MODIS), Landsat-8 Operational Land Imager (OLI) and RapidEye. Images gathered on 10 June 2014 were corrected for the atmospheric effects with the 6SV code. The computed remote sensing reflectance (Rrs) from MODIS and OLI were converted into water quality parameters by adopting a spectral inversion procedure based on a bio-optical model calibrated with optical properties of the lake. The same spectral inversion procedure was applied to RapidEye and to OLI data to map bottom depth. In situ measurements of Rrs and of concentrations of water quality parameters collected in five locations were used to evaluate the models. The bottom depth maps from OLI and RapidEye showed similar gradients up to 7 m (r = 0.72). The results indicate that: (1) the spatial and radiometric resolutions of OLI enabled mapping water constituents and bottom properties; (2) MODIS was appropriate for assessing water quality in the pelagic areas at a coarser spatial resolution; and (3) RapidEye had the capability to retrieve bottom depth at high spatial resolution. Future work should evaluate the performance of the three sensors in different bio-optical conditions.

Phytoplankton response to a plume front in the northern South China Sea

NASA Astrophysics Data System (ADS)

Li, Qian P.; Zhou, Weiwen; Chen, Yinchao; Wu, Zhengchao

2018-04-01

Due to a strong river discharge during April-June 2016, a persistent salinity front, with freshwater flushing seaward on the surface but seawater moving landward at the bottom, was formed in the coastal waters west of the Pearl River estuary (PRE) over the northern South China Sea (NSCS) shelf. Hydrographic measurements revealed that the salinity front was influenced by both the river plume and coastal upwelling. On shipboard nutrient-enrichment experiments with size-fractionation chlorophyll a measurements were taken on both sides of the front as well as in the frontal zone to diagnose the spatial variations of phytoplankton physiology across the frontal system. We also assessed the size-fractionated responses of phytoplankton to the treatment of plume water at the frontal zone and the sea side of the front. The biological impact of vertical mixing or upwelling was further examined by the response of surface phytoplankton to the addition of local bottom water. Our results suggested that there was a large variation in phytoplankton physiology on the sea side of the front, driven by dynamic nutrient fluxes, although P limitation was prevailing on the shore side of the front and at the frontal zone. The spreading of plume water at the frontal zone would directly improve the growth of microphytoplankton, while nano- and picophytoplankton growths could have become saturated at high percentages of plume water. Also, the mixing of bottom water would stimulate the growth of surface phytoplankton on both sides of the front by altering the surface N/P ratio to make it closer to the Redfield stoichiometry. In summary, phytoplankton growth and physiology could be profoundly influenced by the physical dynamics in the frontal system during the spring-summer of 2016.

Multi-year Current Observations on the Shelf Slope off Cape Hatteras, NC

NASA Astrophysics Data System (ADS)

Muglia, M.

2017-12-01

As part of an observing and modeling effort by the North Carolina Renewable Ocean Energy Program to determine if the Gulf Stream is a viable marine hydrokinetic energy resource for the state, upper continental slope current measurements were made over a period of nearly four years off of Cape Hatteras, NC. Velocity profiles were measured by a near-bottom, upward-looking, 150-kHz Acoustic Doppler Current Profiler deployed at a depth of 230-260 m. The mooring was sited at the location where water from the Gulf Stream, Middle Atlantic Bight, South Atlantic Bight, and Slope Sea all converge. Measured tidal amplitudes here are 2 m. These observations are used to consider the temporal variability and vertical structure of the currents at this location at tidal to interannual periods at this complex location. Concurrent near-bottom water mass properties are considered.

Presence, concentrations and risk assessment of selected antibiotic residues in sediments and near-bottom waters collected from the Polish coastal zone in the southern Baltic Sea - Summary of 3years of studies.

PubMed

Siedlewicz, Grzegorz; Białk-Bielińska, Anna; Borecka, Marta; Winogradow, Aleksandra; Stepnowski, Piotr; Pazdro, Ksenia

2018-04-01

Concentrations of selected antibiotic compounds from different groups were measured in sediment samples (14 analytes) and in near-bottom water samples (12 analytes) collected in 2011-2013 from the southern Baltic Sea (Polish coastal zone). Antibiotics were determined at concentration levels of a few to hundreds of ng g -1 d.w. in sediments and ng L -1 in near-bottom waters. The most frequently detected compounds were sulfamethoxazole, trimethoprim, oxytetracycline in sediments and sulfamethoxazole and trimethoprim in near-bottom waters. The occurrence of the identified antibiotics was characterized by spatial and temporal variability. A statistically important correlation was observed between sediment organic matter content and the concentrations of sulfachloropyridazine and oxytetracycline. Risk assessment analyses revealed a potential high risk of sulfamethoxazole contamination in near-bottom waters and of contamination by sulfamethoxazole, trimethoprim and tetracyclines in sediments. Both chemical and risk assessment analyses show that the coastal area of the southern Baltic Sea is highly exposed to antibiotic residues. Copyright © 2017 Elsevier Ltd. All rights reserved.

Flows of Antarctic bottom water through fractures in the southern part of the North Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Morozov, E. G.; Tarakanov, R. Yu.; Makarenko, N. I.

2015-11-01

We study the flows of bottom waters of the Antarctic origin in deep fracture zones of the southern part of the North Mid-Atlantic Ridge. In the autumn of 2014, an expedition onboard the RV Akademik Sergey Vavilov carried out measurements of current velocities and thermohaline properties of bottom water in several quasi-zonal fractures in the southern part of the Northern Mid-Atlantic Ridge, which connect the deep basins of the West and East Atlantic, the Vema Fracture Zone (FZ) (10°50' N) and a group of sub-equatorial fractures: Doldrums (8°15' N), Vernadsky (7°40' N), and a nameless fracture at 7°30' N. The estimates of bottom water (θ < 2.0°C) transport through this group based on measurements from 2014 are approximately 0.28 Sv (1 Sv = 106 m3/s), which is close to 25% of the transport estimate through the Vema FZ (1.20 Sv) obtained in the same expedition. The coldest bottom water temperatures among the investigated fractures were recorded in the Vema FZ.

3-D Wave-Structure Interaction with Coastal Sediments - A Multi-Physics/Multi-Solution Techniques Approach

DTIC Science & Technology

2007-01-01

Stokes (RANS) and the particle finite element method ( PFEM ) will be used in the water/mine/sand domain. Sand and the geomaterials around the sand will...wave propagation over a bottom mine at various time steps (Soil and Foam model) 8 SOLID/FEM SAND/SPH GEOMATERIALS FNPF/BEM FNPF/BEM RANS/ PFEM

Views of Endeavour's payload bay and an Earth limb taken during STS-99

NASA Image and Video Library

2000-02-12

STS099-703-082 (11-22 February 2000) --- Part of the Space Shuttle Endeavour's aft cargo bay, its vertical stabilizer and orbital maneuvering system (OMS) pods are seen in this 70mm frame. Part of Earth's horizon, with an expanse of heavy cloud cover over land and water, is at bottom of frame.

Basic characteristics of leachate produced by various washing processes for MSWI ashes in Taiwan.

PubMed

Yang, Renbo; Liao, Wing-Ping; Wu, Pin-Han

2012-08-15

Approximately 19.2% of Taiwan's municipal solid waste (MSW) that passes through incineration disposal is converted into ashes (including bottom ash and fly ash). Although bottom ash can pass nearly all of the standards of the toxicity characteristic leaching procedure (TCLP), its high chloride content makes its reuse limited; it generally cannot be used as a fine aggregate material in concrete applications. This research examined washing four types of bottom ash (BA) and fly ash (FA) with water to reduce their chloride content. The optimal water intensity for washing pretreated bottom ash was found to be 7-8L of water per kg of bottom ash, and the optimal water intensity for washing untreated fly ash was found to be 20-25 L of water per kg of fly ash. Based on regression analyses of the chloride concentrations of the leachates and their electrical conductivity (EC) values, each MSW incineration plant has its own ash characteristics as well as a specific regression line in bottom or fly ash leachate. Clearly, it is possible to monitor the EC values of the leachates online by estimation from regression equations to determine the chloride concentrations in the leachates. Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.

A global ocean climatological atlas of the Turner angle: implications for double-diffusion and water-mass structure

NASA Astrophysics Data System (ADS)

You, Yuzhu

2002-11-01

The 1994 Levitus climatological atlas is used to calculate the Turner angle (named after J. Stewart Turner) to examine which oceanic water masses are favorable for double-diffusion in the form of diffusive convection or salt-fingering and which are doubly stable. This atlas complements the Levitus climatology. It reveals the major double-diffusive signals associated with large-scale water-mass structure. In total, about 44% of the oceans display double-diffusion, of which 30% is salt-fingering and 14% is diffusive double-diffusion. Results show that various central and deep waters are favorable for salt-fingering. The former is due to positive evaporation minus precipitation, and the latter is due to thermohaline circulation, i.e. the southward spreading of relatively warm, salty North Atlantic Deep Water (NADW) overlying cold, fresh Antarctic Bottom Water. In the northern Indian Ocean and eastern North Atlantic, favorable conditions for salt-fingering are found throughout the water column. The Red Sea (including the Persian Gulf) and Mediterranean Sea are the sources of warm, salty water for the ocean. As consequence, temperature and salinity in these outflow regions both decrease from the sea surface to the bottom. On the other hand, ocean currents are in general sluggish in these regions. In the polar and subpolar regions of Arctic and Antarctic, Okhotsk Sea, Gulf of Alaska, the subpolar gyre of the North Pacific, the Labrador Sea, and the Norwegian Sea, the upper layer water is favorable for diffusive convection because of high latitude surface cooling and ice melting. Weak and shallow diffusive convection is also found throughout tropical regions and the Bay of Bengal. The former is due to excessive precipitation over evaporation and rain cooling, and the latter is due to both precipitation and river runoff. Diffusive convection in the ocean's interior is unique to the South Atlantic between Antarctic Intermediate Water and upper NADW (uNADW). It is the consequence of the intrusive equatorward flow of upper Circumpolar Deep Water, which carries with it the minimum temperature and very low salinity overlying warm, salty uNADW.

Terrestrial water cycle induced meridional overturning circulation variability over the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Hsu, C. W.; Velicogna, I.

2016-12-01

Terrestrial water cycle has a significant role in the long-term changes of Atlantic meridional overturning circulation (AMOC). With the fresh water input over the ocean from the river runoff or ice melting at the higher latitude, AMOC transport has been predicted to slow down at the end of the century. We compare ocean bottom pressure measured from the GRACE satellite data with the conventional density derived transport observations from the RAPID MOC/MOCHA array to study the impact of the terrestrial water cycle on the seasonal and inter annual AMOC variability detected by the RAPID MOC/MOCHA array observations. We propose that the observed short-term variability is due to coupling of wind driven and terrestrial water cycle changes. We show that the proposed mechanism explains a significant portion of the transport variance and we present new possible mechanism that can explain the residual transport signal in AMOC.

Assessment of chemical and biological significance of arsenical species in the Maurice River drainage basin (N. J. ). Part I. Distribution in water and river and lake sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faust, S.D.; Winka, A.J.; Belton, T.

1987-01-01

Levels of arsenic were determined in the bottom sediments and waters of the Maurice River, Blackwater Branch, and Union Lake, (N.J.) that were contaminated by a local chemical industry. This was the only known source of the arsenic. Levels of total arsenic in the sediments and waters were determined quarterly over the course of one year. Sediments were extracted for water soluble and total extractable arsenic fractions and partitioned into four species: monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA), arsenite (As(III)), and arsenate (As(V)). In Union Lake at a shallow sandy sediment site, As (V) predominates. In organic sediments, As (III)more » or (V) predominate depending upon the dissolved oxygen content of the overlying waters. The oxidations state of the arsenic was affected also by the seasonal lake cycles of stratifying or mixing.« less

Narrow-field-of-view bathymetrical lidar: theory and field test

NASA Astrophysics Data System (ADS)

Feygels, Viktor I.; Wright, C. Wayne; Kopilevich, Yuri I.; Surkov, Alexey I.

2003-11-01

The purpose of this paper is to derive a reliable theory to predict the performance of a narrow-FOV bathymetric lidar. A fundamental discrepancy between the theoretical estimate and experimental results was the inspiration for the work presented here Meeting oceanographic mapping requirements is a critically important goal for littoral laser bathymetry. In contrast to traditional airborne lidar system which are optimized for recovering signals from the deepest possible waters , the above challenge may be met with a radical narrowing to the lidar transmit beam and receiver field of view (FOV) employed in EAARL (Experimental Advanced Airborne Research Lidar, NASA). In this paper we discuss theoretical analysis carried out on the basis of a sophisticated "multiple-forward scattering and single-backscattering model" for lidar return signals allows a quantitative estimation of the advantages of a narrow-FOV system over traditional bathymetric lidars (SHOALS-400, SHOALS-100, LADS Mk II) when used in clear shallow-water cases. Some of those advantages are: ¸ Increase in bottom definition (or reduced false-alarm probability) due to the enhanced contrast of the bottom return over the background backscatter from the water column, ¸ Enhancement in depth measurement accuracy resulting from narrower bottom return pulse width, ¸ Reduction of post-surface return effects in the lidar photo-multiplier detector due to a more rapid decay of water column backscatter, ¸ Greatly improved rejection of ambient light permitting lidar operations in all zenith sun angles and flight directions. The model computations make it possible to estimate the maximal operational depth for the system under consideration by the implementation of statistical theory of detectability. These computations depend on the prevailing seawater optical properties and lidar parameters. The theoretical predictions are compared with results obtained in the field test of the EAARL system carried out in Florida Keys in 2001.

Temporal and spatial variations in suspended matter in continental shelf and slope waters off the north-eastern United States

USGS Publications Warehouse

Bothner, Michael H.; Parmenter, Carol M.; Milliman, John D.

1981-01-01

Seston in waters of Georges Bank originates primarily from biological production and from resuspension of bottom sediments. The concentrations of suspended matter observed on the central shoals are more influenced by storms than by seasonal changes. Winter storms produce highest concentrations of non-combustible material throughout the water column, and summer storms appear to increase biological production by mixing additional nutrients into the photic zone. On the south-east flank of the bank, in water depths between 80 and 200 in, the concentrations of total suspended matter and non-combustible material show little variation compared with the central shoals, and storm effects are far less noticeable.Highest concentrations (>15 mg 1−1) of suspended matter occur in bottom waters south of Nantucket Island after winter storms and appear to be primarily resuspended bottom sediment. Resuspended sediment is also common in near-bottom waters of the south-western Gulf of Maine, and occasionally near the intersection of the shelf/slope water mass front and the bottom.Seasonal variations were observed in the distribution and species composition of phytoplankton. Coccoliths are predominant on the central bank during the winter, but during the spring and summer they are concentrated on the eastern flank at deeper depths.

Gas buildup in Lake Nyos, Cameroon: The recharge process and its consequences

USGS Publications Warehouse

Evans, William C.; Kling, G.W.; Tuttle, M.L.; Tanyileke, G.; White, L.D.

1993-01-01

The gases dissolved in Lake Nyos, Cameroon, were quantified recently (December 1989 and September 1990) by two independent techniques: in-situ measurements using a newly designed probe and laboratory analyses of samples collected in pre-evacuated stainless steel cylinders. The highest concentrations of CO2 and CH4 were 0.30 mol/kg and 1.7 mmol/kg, respectively, measured in cylinders collected 1 m above lake bottom. Probe measurements of in-situ gas pressure at three different stations showed that horizontal variations in total dissolved gas were negligible. Total dissolved-gas pressure near the lake bottom is 1.06 MPa (10.5 atm), 50% as high as the hydrostatic pressure of 2.1 MPa (21 atm). Comparing the CO2 profile constructed from the 1990 data to one obtained in May 1987 shows that CO2 concentrations have increased at depths to below 150 m. Based on these profiles, the average rate of CO2 input to bottom waters was 2.6 ?? 108 mol/a. Increased deep-water temperatures require an average heat flow of 0.32 MW into the hypolimnion over the same time period. The transport rates of CO2, heat, and major ions into the hypolimnion suggest that a low-temperature reservoir of free CO2 exists a short distance below lake bottom and that convective cycling of lake water through the sediments is involved in transporting the CO2 into the lake from the underlying diatreme. Increased CH4 concentrations at all depths below the oxycline and a high 14C content (41% modern) in the CH4 4 m above lake bottom show that much of the CH4 is biologically produced within the lake. The CH4 production rate may vary with time, but if the CO2 recharge rate remains constant, CO2 saturation of the entire hypolimnion below 50 m depth would require ???140 a, given present-day concentrations. ?? 1993.

Developing Improved Water Velocity and Flux Estimation from AUVs - Results From Recent ASTEP Field Programs

NASA Astrophysics Data System (ADS)

Kinsey, J. C.; Yoerger, D. R.; Camilli, R.; German, C. R.

2010-12-01

Water velocity measurements are crucial to quantifying fluxes and better understanding water as a fundamental transport mechanism for marine chemical and biological processes. The importance of flux to understanding these processes makes it a crucial component of astrobiological exploration to moons possessing large bodies of water, such as Europa. Present technology allows us to obtain submerged water velocity measurements from stationary platforms; rarer are measurements from submerged vehicles which possess the ability to autonomously survey tens of kilometers over extended periods. Improving this capability would also allow us to obtain co-registered water velocity and other sensor data (e.g., mass spectrometers, temperature, oxygen, etc) and significantly enhance our ability to estimate fluxes. We report results from 4 recent expeditions in which we measured water velocities from autonomous underwater vehicles (AUVs) to help quantify flux in three different oceanographic contexts: hydrothermal vent plumes; an oil spill cruise responding to the 2010 Deepwater Horizon blowout; and two expeditions investigating naturally occurring methane seeps. On all of these cruises, we directly measured the water velocities with an acoustic Doppler current profiler (ADCP) mounted on the AUV. Vehicle motion was corrected for using bottom-lock Doppler tracks when available and, in the absence of bottom-lock, estimates of vehicle velocity based on dynamic models. In addition, on the methane seep cruises, we explored the potential of using acoustic mapping sonars, such as multi-beam and sub-bottom profiling systems, to localize plumes and indirectly quantify flux. Data obtained on these expeditions enhanced our scientific investigations and provides data for future development of algorithms for autonomously processing, identifying, and classifying water velocity and flux measurements. Such technology will be crucial in future astrobiology missions where highly constrained bandwidth will require robots to possess sufficient autonomy to process and react to data independent of human interpretation and interaction.

Mass-physical properties of surficial sediments on the Rhoˆne continental margin: implications for the nepheloid benthic layer

NASA Astrophysics Data System (ADS)

Chassefiere, Bernard

1990-09-01

Mass-physical properties of the surficial (upper 5 m) sediments on the Gulf of Lions continental margin were analysed, from more than 100 short (1 m) and longer (5 m) cores obtained during several cruises. Data include water content, unit weight, Atterberg limits (liquid limit, plastic limit, plasticity index), shear strength and compression index, and are used to determine: first, the mass property distribution, according to the main parameters influencing mass-physical properties; the relationships between these properties and the nepheloid layer on the shelf. The shoreline (lagoons) and inner shelf are characterized by low density and shear strength and high water content deposits, due to electrochemical flocculation of the sediment. The outer shelf is blanketed by higher density and shear strength and lower water content deposits generated by normal settling of suspended particles. On the inner shelf, during river peak discharges, a short-term thin bottom layer of "yogurt-like" [ FASS (1985) Geomarine Letters, 4, 147-152; FASS (1986) Continental Shelf Research, 6, 189-208] fluid-mud (unit weight lower than 1.3 mg m -3) is supplied, by a bottom nepheloid layer. During stormy periods, this "yogurt-like" layer (about 10 cm thick) partly disappears by resuspension of suspended particulate matter; this is advected, in the bottom nepheloid layer, over the shelf and the canyons within the upper slope.

Impact of eutrophication on shallow marine benthic foraminifers over the last 150 years in Osaka Bay, Japan

USGS Publications Warehouse

Tsujimoto, Akira; Nomura, Ritsuo; Yasuhara, Moriaki; Yamazaki, Hideo; Yoshikawa, Shusaku

2006-01-01

High-resolution foraminiferal analysis was conducted on a short sediment core from the inner part of Osaka Bay, Japan. Changes in foraminiferal assemblages were associated with eutrophication, bottom water hypoxia, and changes in red tide-causing algae. Before the 1920s, the calcareous species Ammonia beccarii, and the agglutinated species Eggerella advena and Trochammina hadai were rare, but calcareous foraminifers in general were abundant. Between the 1920s and 1940s, calcareous foraminifers decreased abruptly in abundance, while A. beccarii, E. advena and T. hadai increased in abundance. This faunal change corresponded in time to an increase in nutrients flowing in through the Yodo River, and bottom water hypoxia related to eutrophication. In the 1960s and 1970s, A. beccarii, E. advena and T. hadai further increased in abundance to become dominant, and many calcareous foraminifers nearly disappeared, corresponding to increasing bottom water hypoxia related to the rapid increase in discharged nutrients during the high economic growth period from 1953 to 1971. After the 1990s, A. beccarii decreased rapidly in abundance and E. advena and Uvigerinella glabra increased in abundance. The main components of red tide-causing algae changed from dinoflagellates to diatoms in the 1980s through 1990s, thus there was a change in the food supply to the benthos, which may have caused the increase in abundance of E. advena and U. glabra.

Factors influencing release of phosphorus from sediments in a high productive polymictic lake system.

PubMed

Solim, S U; Wanganeo, A

2009-01-01

Phosphorus (P) release rates from bottom sediments are high (20.6 mg/m(2)/day) in Dal Lake (India), a polymictic hyper-eutrophic lake. These gross release rates occur over a period of 72 days during summer only. Likewise, a net internal load of 11.3 tons was obtained from mass balance estimates. Significant proportion i.e. approximately 80% of 287.3 tons/yr of nitrate nitrogen (NO(3)-N) load is either eliminated by denitrification or gets entrapped for a short period in high macrophyte biomass of 3.2 kg/m(2) f.w., which eventually get decomposed and nitrogen (N) is released back. These processes result in low lake water NO(3)-N concentrations which potentially influence sediment phosphorus (P) release. Especially, nitrate nitrogen (NO(3)-N) <500 microg/L in the lake waters were associated with high P concentrations. Phosphorus was also observed to increase significantly in relation to temperature and pH, and it seems likely that release of phosphorus and ammonical nitrogen (NH(4)-N) depend on decomposition of rich reserves of organic matter (893 tons d.w. in superficial 10-cm bottom sediment layer). Lake P concentrations were significantly predicted by a multivariate regression model developed for the lake. This study describes significance of various lake water variables in relation to P-release from bottom sediments.

Reactive transport modeling of nitrogen in Seine River sediments

NASA Astrophysics Data System (ADS)

Akbarzadeh, Z.; Laverman, A.; Raimonet, M.; Rezanezhad, F.; Van Cappellen, P.

2016-02-01

Biogeochemical processes in sediments have a major impact on the fate and transport of nitrogen (N) in river systems. Organic matter decomposition in bottom sediments releases inorganic N species back to the stream water, while denitrification, anammox and burial of organic matter remove bioavailable N from the aquatic environment. To simulate N cycling in river sediments, a multi-component reactive transport model has been developed in MATLAB®. The model includes 3 pools of particulate organic N, plus pore water nitrate, nitrite, nitrous oxide and ammonium. Special attention is given to the production and consumption of nitrite, a N species often neglected in early diagenetic models. Although nitrite is usually considered to be short-lived, elevated nitrite concentrations have been observed in freshwater streams, raising concerns about possible toxic effects. We applied the model to sediment data sets collected at two locations in the Seine River, one upstream, the other downstream, of the largest wastewater treatment plant (WWTP) of the Paris conurbation. The model is able to reproduce the key features of the observed pore water depth profiles of the different nitrogen species. The modeling results show that the presence of oxygen in the overlying water plays a major role in controlling the exchanges of nitrite between the sediments and the stream water. In August 2012, sediments upstream of the WWTP switch from being a sink to a source of nitrite as the overlying water becomes anoxic. Downstream sediments remain a nitrite sink in oxic and anoxic conditions. Anoxic bottom waters at the upstream location promote denitrification, which produces nitrite, while at the downstream site, anammox and DNRA are important removal processes of nitrite.

Innovative High-Accuracy Lidar Bathymetric Technique for the Frequent Measurement of River Systems

NASA Astrophysics Data System (ADS)

Gisler, A.; Crowley, G.; Thayer, J. P.; Thompson, G. S.; Barton-Grimley, R. A.

2015-12-01

Lidar (light detection and ranging) provides absolute depth and topographic mapping capability compared to other remote sensing methods, which is useful for mapping rapidly changing environments such as riverine systems. Effectiveness of current lidar bathymetric systems is limited by the difficulty in unambiguously identifying backscattered lidar signals from the water surface versus the bottom, limiting their depth resolution to 0.3-0.5 m. Additionally these are large, bulky systems that are constrained to expensive aircraft-mounted platforms and use waveform-processing techniques requiring substantial computation time. These restrictions are prohibitive for many potential users. A novel lidar device has been developed that allows for non-contact measurements of water depth down to 1 cm with an accuracy and precision of < 1 cm by exploiting the polarization properties of the light-surface interaction. This system can transition seamlessly from ranging over land to shallow to deep water allowing for shoreline charting, measuring water volume, mapping bottom topology, and identifying submerged objects. The scalability of the technique opens up the ability for handheld or UAS-mounted lidar bathymetric systems, which provides for potential applications currently unavailable to the community. The high laser pulse repetition rate allows for very fine horizontal resolution while the photon-counting technique permits real-time depth measurement and object detection. The enhanced measurement capability, portability, scalability, and relatively low-cost creates the opportunity to perform frequent high-accuracy monitoring and measuring of aquatic environments which is crucial for understanding how rivers evolve over many timescales. Results from recent campaigns measuring water depth in flowing creeks and murky ponds will be presented which demonstrate that the method is not limited by rough water surfaces and can map underwater topology through moderately turbid water.

MEANS FOR SHIELDING AND COOLING REACTORS

DOEpatents

Wigner, E.P.; Ohlinger, L.A.; Young, G.J.; Weinberg, A.M.

1959-02-10

Reactors of the water-cooled type and a means for shielding such a rcactor to protect operating personnel from harmful radiation are discussed. In this reactor coolant tubes which contain the fissionable material extend vertically through a mass of moderator. Liquid coolant enters through the bottom of the coolant tubes and passes upwardly over the fissionable material. A shield tank is disposed over the top of the reactor and communicates through its bottom with the upper end of the coolant tubes. A hydrocarbon shielding fluid floats on the coolant within the shield tank. With this arrangements the upper face of the reactor can be opened to the atmosphere through the two superimposed liquid layers. A principal feature of the invention is that in the event radioactive fission products enter thc coolant stream. imposed layer of hydrocarbon reduces the intense radioactivity introduced into the layer over the reactors and permits removal of the offending fuel material by personnel shielded by the uncontaminated hydrocarbon layer.

210Pb in the western Indian Ocean: distribution, disequilibrium, and partitioning between dissolved and particulate phases

NASA Astrophysics Data System (ADS)

Chung, Y.

1987-09-01

Dissolved 210Pb profiles are presented for 13 GEOSECS stations in the western Indian Ocean. In surface water away from high southern latitudes, 210Pb is in excess over 226Ra due to the atmospheric fallout from decay of 222Rn. Except in the Circumpolar region, the dissolved 210Pb profiles display a gentle mid-depth maximum similar to the corresponding 226Ra profiles. The 210Pb/ 226Ra activity ratio ranges from 1.6 in the surface water east of Madagascar to 0.4 or less in the bottom water of all the basins. The lowest ratio observed was 0.1 in the Gulf of Aden very close to the continental land mass. A ratio of 0.6 divides the western Indian Ocean horizontally into two portions, with the contour at shallower depth in the north than in the south. The deep water disequilibrium is thus more extensive north of Madagascar than south of it. It appears that locality and bottom topography play a strong role in controlling the distributions of 210Pb and 226Ra as well as their extent of disequilibrium in the water column. The mean residence time for Pb with respect to particulate and boundary scavenging in the deep water ranges from about 15 to 75 years.

Distribution of Arctic and Pacific copepods and their habitat in the northern Bering Sea and Chukchi Sea

NASA Astrophysics Data System (ADS)

Sasaki, H.; Matsuno, K.; Fujiwara, A.; Onuka, M.; Yamaguchi, A.; Ueno, H.; Watanuki, Y.; Kikuchi, T.

2015-11-01

The advection of warm Pacific water and the reduction of sea-ice extent in the western Arctic Ocean may influence the abundance and distribution of copepods, i.e., a key component in food webs. To understand the factors affecting abundance of copepods in the northern Bering Sea and Chukchi Sea, we constructed habitat models explaining the spatial patterns of the large and small Arctic copepods and the Pacific copepods, separately, using generalized additive models. Copepods were sampled by NORPAC net. Vertical profiles of density, temperature and salinity in the seawater were measured using CTD, and concentration of chlorophyll a in seawater was measured with a fluorometer. The timing of sea-ice retreat was determined using the satellite image. To quantify the structure of water masses, the magnitude of pycnocline and averaged density, temperature and salinity in upper and bottom layers were scored along three axes using principal component analysis (PCA). The structures of water masses indexed by the scores of PCAs were selected as explanatory variables in the best models. Large Arctic copepods were abundant in the water mass with high salinity water in bottom layer or with cold/low salinity water in upper layer and cold/high salinity water in bottom layer, and small Arctic copepods were abundant in the water mass with warm/saline water in upper layer and cold/high salinity water in bottom layers, while Pacific copepods were abundant in the water mass with warm/saline in upper layer and cold/high salinity water in bottom layer. All copepod groups were abundant in areas with deeper depth. Although chlorophyll a in upper and bottom layers were selected as explanatory variables in the best models, apparent trends were not observed. All copepod groups were abundant where the sea-ice retreated at earlier timing. Our study might indicate potential positive effects of the reduction of sea-ice extent on the distribution of all groups of copepods in the Arctic Ocean.

Diurnal dynamics of the CO2 concentration in water of the coastal zone of lake Baikal in the ice period (testing of the DIEL - CO2 method for assessment of lake metabolic rate)

NASA Astrophysics Data System (ADS)

Panchenko, M. V.; Domysheva, V. M.; Pestunov, D. A.; Sakirko, M. V.; Ivanov, V. G.; Shamrin, A. M.

2017-11-01

Results of three long cycles of 24-hour measurements of the carbon dioxide content in the surface and bottom water in the ice period of 2014-2016 in the Baikal coastal zone are analyzed. The diurnal dynamics of the CO2 concentration in the subglacial water, in which photosynthesis plays the leading role, is described. It is found that, in comparison with the surface subglacial water (that is, directly adjacent to the ice bottom), the more pronounced diurnal rhythm of CO2 is observed in the bottom layer in all realizations. This rhythm is well correlated with pyranometer readings. The data on the diurnal dynamics of CO2 are used to estimate the gross primary production in the bottom water with the DIEL method based on the analysis of temporal variability of the carbon dioxide concentration in water in situ.

Bottom-Interating Ocean Acoustics. Proceedings of a Conference held at SACLANTCEN on 9-13 June 1980.

DTIC Science & Technology

1980-07-15

scattering by John H. Hanrahan (M) 11 Some bottom-reflection loss anomalies near grazing and their effect on propagation in shallow water by Ole F. Hastrup (Q...SACLANTCEN CP-27 11 SOME BOTTOM-REFLECTION LOSS ANOMALIES NEAR GRAZING AND THEIR EFFECT ON PROPAGATION IN SHALLOW WATER by Ole F. Hastrup SACLANT ASW

Best Practices for In-Situ Sediment-Water Incubations with Benthic Landers

NASA Astrophysics Data System (ADS)

Tengberg, Anders; Kononets, Mikhail; Hall, Per; Nilsson, Madeleine; Ekeroth, Nils

2017-04-01

Biological, chemical, physical and geological processes that take place at the seafloor are crucial in influencing and regulating many aquatic environments. One method to estimate exchange rates, fluxes, between the sediment and the overlying water is in-situ sediment-water incubations using autonomous chamber landers. As for all field sampling and measurements best practices methods are needed to obtain high quality data. With experiences form many years usage of the Gothenburg autonomous bottom lander systems this presentation will describe some of the experimental work that has been done with focus on quality control and data evaluation methods.

Thermohaline variability and Antarctic bottom water formation at the Ross Sea shelf break

NASA Astrophysics Data System (ADS)

Budillon, Giorgio; Castagno, Pasquale; Aliani, Stefano; Spezie, Giancarlo; Padman, Laurie

2011-10-01

We use hydrological and current meter data collected in the Ross Sea, Antarctica between 1995 and 2006 to describe the spatial and temporal variability of water masses involved in the production of Antarctic Bottom Water (AABW). Data were collected in two regions of known outflows of dense shelf water in this region; the Drygalski Trough (DT) and the Glomar-Challenger Trough (GCT). Dense shelf water just inshore of the shelf break is dominated by High Salinity Shelf Water (HSSW) in the DT and Ice Shelf Water (ISW) in the GCT. The HSSW in the northern DT freshened by ˜0.06 in 11 y, while the ISW in the northern GCT freshened by ˜0.04 in 8 y and warmed by ˜0.04 °C in 11 y, dominated by a rapid warming during austral summer 2001/02. The Antarctic Slope Front separating the warm Circumpolar Deep Water (CDW) from the shelf waters is more stable near GCT than near DT, with CDW and mixing products being found on the outer DT shelf but not on the outer GCT shelf. The different source waters and mixing processes at the two sites lead to production of AABW with different thermohaline characteristics in the central and western Ross Sea. Multi-year time series of hydrography and currents at long-term moorings within 100 km of the shelf break in both troughs confirm the interannual signals in the dense shelf water and reveal the seasonal cycle of water mass properties. Near the DT the HSSW salinities experienced maxima in March/April and minima in September/October. The ISW in the GCT is warmest in March/April and coolest between August and October. Mooring data also demonstrate significant high-frequency variability associated with tides and other processes. Wavelet analysis of near-bottom moored sensors sampling the dense water cascade over the continental slope west of the GCT shows intermittent energetic pulses of cold, dense water with periods from ˜32 h to ˜5 days.

New insights into submarine geomorphology and depositional processes along the George V Land continental slope and upper rise (East Antarctica)

NASA Astrophysics Data System (ADS)

de Santis, Laura

2010-05-01

Swath bathymetry collected by the Italian Antarctic Program (PNRA), in the offshore of the George Vth Land, document evidence of cascading, cold and dense bottom currents, inside continental slope canyons, and suggest an active role of the sea floor morphology on modern and ancient process. The continental slope is incised by canyons locally heading to the shelf edge and bounding sedimentary ridges of Miocene age(ref1,2). Erosion by bottom water masses, up to present times, exhumed or prevented the burial of such relict sedimentary ridges originated by glacial processes. Dense shelf water is formed by coastal polynyas and is exported over the shelf break to produce Antarctic Bottom Water (AABW)(ref3,4). This locally formed AABW (often referred to as Adélie Land Bottom Water) is detected by CTD and mooring measurements up to about 3200 m of depth, in the Jussieu canyon and further to the west(ref5). The speed of the ALBW is enough to transport fine sand and silt from shallow to deep water. Evidence for exporting sediment off the shelf via bottom water, through the Holocene, is inferred by sedimentological and geophysical studies(ref6,7). Morphologic and geological data in the slope and rise confirm that the Jussieu canyon is a main conduit of high energetic bottom current, in present times as well as in the past(ref1,7). Coarse grain material and turbidites (up to 1 meter thick) were sampled from the canyon levees at 2500 and 3000 meters of water depth(ref1). At a depth of 2600 m, the Jussieu canyon converges with two canyons into a single branch, showing a meandering trend, up to about 3200 m of water depth. The asymmetry of the meandering section and the internal geometry of its levees are typical expressions of differential erosion and deposition from downslope flows. Sediment waves characterise the western flank of the Wega Channel, at depth of 2400-2800 meters, to the east of the Jussieu canyon(ref1). The waves are composed by fine grained sediments whose source is identified in the George V Land rocks and in the continental shelf(ref8). The waves formed under the action of weak and constant, downslope bottom current, since MIS 11(ref9,10), documenting the occurrence of shelf originated bottom current also in this channel. No significant component of shelf-originated, bottom water is detected at the head of the WEGA channel. The current that originated the sediment wave field in the WEGA channel must then be fed by the ALBW flowing inside the Jussieu branches in the upper slope, deviated to the east. This process likely happens at water depth of about 2600, where the continental slope decreases its steepness and the branches of the upper Jussieu canyon converge into the single meandering channel-levee, in the lower rise. This abrupt morphologic bend likely forces part of the cascading water mass confined inside the canyons to thickens and to overspill the flanks and to flow down the WEGA channel, until it reaches equilibrium with its surroundings. ref1: Harris, Brancolini, Bindoff, De Santis (eds.), Deep-Sea Research II (2003),volume50,n.8-9. ref2: Caburlotto A. et al. (2006), Quaternary Science Reviews, 25,3029-3049. ref3: Rintoul S.R. (1998). AGU, Antarctic Research Series 75,51-171. ref4: Williams G.D. et al. (2008), Journal of Geophysical Research, Volume113,C04039. ref5: Williams G.D. et al. (2010), Journal of Geophysical Research, in-press. ref6: Harris PT et al. (2001) Marine Geology 179, 1-8. ref7: Escutia C. et al. (2000) Journal of Sedimentary Research 70 (1), 84-93. ref8: Damiani D. et al. (2006) Marine Geology 226, 281- 295 ref9: Caburlotto A. et al. (2009). International Journal of Earth Science, in-press. ref10: Macrì P. et al. (2005). Physics of the Earth and Planetary Interiors 151 (2005) 223-242

High Concentration of Methane and Magnificent gas Plumes Over gas Hydrate Field in the Eastern Margin of Japan Sea

NASA Astrophysics Data System (ADS)

Ishida, Y.; Matsumoto, R.; Hiruta, A.; Aoyama, C.; Tomaru, H.; Hiromatsu, M.

2005-12-01

Gas hydrates and prominent pockmarks have been observed on the Umitaka Spur in the eastern margin of Japan Sea, at the depth of about 900 m.Magnificent methane plumes, 550 to 600 m high, were detected by echo sounder for fish school, and massive gas hydrates were recovered by piston coring during the UT04 cruise of R/V Umitaka-maru (2004). The seawater over this area was collected by CTD and the samples of interstitial waters were extracted from sediment cores by hydraulic squeezer. The ratio of methane to ethane concentration (C1/C2) and the isotopic (δ 13C) composition of methane in the plume sites are less than 103 and from -40 to -50 (‰ PDB) respectively, suggesting that the origin of such gases are mostly thermogenic, whereas the gases in the sediments away from plumes are mostly microbial. The seawater samples demonstrated anomalously high concentration of methane over the plume sites. Maximum concentration is 160nmol/L above the methane plume site. The methane concentration values of most samples ranged from 4 to 6nmol/L. When it compared with the Nankai Trough (1 to 4nmol/L), even the base level methane is quite high. Seawater samples collected at the depth of 200 m exhibit sharp anomalies of 16 to 34nmol/L. With the intension to check the possibility of the inflow from the shelf and river waters, we collected surface waters far away from the Umitaka spur. Methane concentration was only 7nmol/L. Therefore, we conclude that anomalously high concentration at 200 m level over the spur is not likely to be explained by inflow of shelf waters, but also by methane seeps. The temperature of waters are extremely low from 0.25°C to 1.0°C below 300 m, then abruptly increases in shallow waters to about 25°C at surface water. Thus, bottom and intermediate waters are within the stability condition of methane hydrate. Under these conditions, gases from the sea floor would form gas hydrate within bottom water mass. Gas hydrate crystals would float up shallow to the water mass where they dissociate to supply methane at around 300 m due to abrupt temperature increase.

Quantification of soil erosion and transport processes in the in the Myjava Hill Land

NASA Astrophysics Data System (ADS)

Hlavcová, Kamila; Kohnová, Silvia; Velisková, Yvetta; Studvová, Zuzana; Socuvka, Valentin; Németová, Zuzana; Duregová, Maria

2017-04-01

The aim of the study is a complex analysis of soil erosion processes and proposals for erosion control in the region of the Myjava Hill Land located in western Slovakia. The Myjava Hill Land is characteristic of quick runoff response, intensive soil erosion by water and related muddy floods, which are determined by both natural and socio-economic conditions. In this paper a case study in the Svacenický Creek catchment, with a focus on the quantification of soil loss from the agriculturally arable lands and sediment transport to the dry water reservoir (polder) of the Svacenický Creek is presented. Erosion, sediment transport, and the deposition of sediments in the water reservoir represent a significant impact on its operation, mainly with regard to reducing its accumulation volume. For the analysis of the soil loss and sediment transport from the Svacenický Creek catchment, the Universal Soil Loss Equation, the USLE 2D, and the Sediment Delivery Ratio (SDR) models were applied. Because the resulting values of the soil loss exceeded the values of the tolerated soil loss, erosion control measures by strip cropping were designed. Strip cropping is based on altering crop strips with protective (infiltration) strips. The effectiveness of the protective (infiltration) strips for reducing runoff from the basin by the SCS-CN method was estimated. Monitoring the morphological parameters of bottom sediments and their changes over time is crucial information in the field of water reservoir operations. In September 2015, the AUV EcoMapper was used to gather the data information on the Svacenický Creek reservoir. The data includes information about the sediment depths and parameters of the water quality. The results of the surveying are GIS datasets and maps, which provide a higher resolution of the bathymetric data and contours of the bottom reservoir. To display the relief of the bottom, the ArcMap 10.1. software was used. Based on the current status of the bottom bathymetry, the current status of the clogging of the reservoir was evaluated. After an evaluation of all the analyses, we can conclude that within five years of the acceptance run, 10,515 m3 of bottom sediments accumulated in the Svacenický Creek reservoir.

Sediment transport in the presence of large reef bottom roughness

USGS Publications Warehouse

Pomeroy, Andrew; Lowe, Ryan J.; Ghisalberti, Marco; Storlazzi, Curt; Symonds, Graham; Roelvink, Dano

2017-01-01

The presence of large bottom roughness, such as that formed by benthic organisms on coral reef flats, has important implications for the size, concentration, and transport of suspended sediment in coastal environments. A 3 week field study was conducted in approximately 1.5 m water depth on the reef flat at Ningaloo Reef, Western Australia, to quantify the cross-reef hydrodynamics and suspended sediment dynamics over the large bottom roughness (∼20–40 cm) at the site. A logarithmic mean current profile consistently developed above the height of the roughness; however, the flow was substantially reduced below the height of the roughness (canopy region). Shear velocities inferred from the logarithmic profile and Reynolds stresses measured at the top of the roughness, which are traditionally used in predictive sediment transport formulations, were similar but much larger than that required to suspend the relatively coarse sediment present at the bed. Importantly, these stresses did not represent the stresses imparted on the sediment measured in suspension and are therefore not relevant to the description of suspended sediment transport in systems with large bottom roughness. Estimates of the bed shear stresses that accounted for the reduced near-bed flow in the presence of large roughness vastly improved the relationship between the predicted and observed grain sizes that were in suspension. Thus, the impact of roughness, not only on the overlying flow but also on bed stresses, must be accounted for to accurately estimate suspended sediment transport in regions with large bottom roughness, a common feature of many shallow coastal ecosystems.

Results of an adaptive environmental assessment modeling workshop concerning potential impacts of drilling muds and cuttings on the marine environment

USGS Publications Warehouse

Auble, Gregor T.; Andrews, Austin K.; Ellison, Richard A.; Hamilton, David B.; Johnson, Richard A.; Roelle, James E.; Marmorek, David R.

1983-01-01

Drilling fluids or "muds" are essential components of modern drilling operations. They provide integrity for the well bore, a medium for removal of formation cuttings, and lubrication and cooling of the drill bit and pipe. The modeling workshop described in this report was conducted September 14-18, 1981 in Gulf Breeze, Florida to consider potential impacts of discharged drilling muds and cuttings on the marine environment. The broad goals of the workshop were synthesis of information on fate and effects, identification of general relationships between drilling fluids and the marine environment, and identification of site-specific variables likely to determine impacts of drilling muds and cuttings in various marine sites. The workshop was structured around construction of a model simulating fate and effects of discharges from a single rig into open water areas of the Gulf of Mexico, and discussion of factors that might produce different fate and effects in enclosed areas such as bays and estuaries. The simulation model was composed of four connected submodels. A Discharge/Fate submodel dealt with the discharge characteristics of the rig and the subsequent fate of discharged material. Three effects submodels then calculated biological responses at distances away from the rig for the water column, soft bottom benthos (assuming the rig was located over a soft bottom environment), and hard bottom benthos (assuming the rig was located over a hard bottom environment). The model focused on direct linkages between the discharge and various organisms rather than on how the marine ecosystem itself is interconnected. Behavior of the simulation model indicated relatively localized effects of drilling muds and cuttings discharged from a single platform into open water areas. Water column fate and effects were dominated by rapid dilution. Effects from deposition of spent mud and cuttings were spatially limited with relatively rapid recovery, especially in soft bottom benthic communities which were conceptualized as being adapted to frequent storms. This behavior was generated by the set of assumptions about linkages and functional relationships used to construct the model. Areas of uncertainty included methods for extrapolating 96-hr LC50 so results to exposures of varying lengths and concentrations; recovery rates of benthic communities; responses to various depths and rates of burial; fate and effects of the plume in relationship to stratification layers; and long-term and sub-lethal effects of slightly elevated concentrations of discharged materials. Evaluation of the assumptions of the Soft Bottom Submodel suggest that the assumptions used may have been relatively liberal estimates of resiliency of these communities. Discussion of "closed" water bodies such as bays and estuaries indicated several reasons to expect different and more complex fate and effects behavior in these areas. These factors included different species and communities (such as aquatic macrophytes and oyster beds), more complex circulation and stratification patterns, and potentially more active resuspension processes. Much of the possible difference in behavior in these areas centers around the extent to which they are “closed” or in the relative residence times of water and sediments in these areas as they determine the long-term dispersion of discharged material. Despite the complexity and variability of these areas, a large body of knowledge (such as that concerning fate and physical effects of dredge spoil) that could be effectively employed in analysis of potential fate and physical effects in enclosed areas was identified.

Oxic to anoxic transition in bottom waters during formation of the Citronen Fjord sediment-hosted Zn-Pb deposit, North Greenland

USGS Publications Warehouse

Slack, John F.; Rosa, Diogo; Falck, Hendrik

2015-01-01

Bulk geochemical data acquired for host sedimentary rocks to the Late Ordovician Citronen Fjord sediment-hosted Zn-Pb deposit in North Greenland constrain the redox state of bottom waters prior to and during sulphide mineralization. Downhole profiles for one drill core show trends for redox proxies (MnO, Mo, Ce anomalies) that suggest the local basin bottom waters were initially oxic, changing to anoxic and locally sulphidic concurrent with sulphide mineralization. We propose that this major redox change was caused by two broadly coeval processes (1) emplacement of debris-flow conglomerates that sealed off the basin from oxic seawater, and (2) venting of reduced hydrothermal fluids into the basin. Both processes may have increased H2S in bottom waters and thus prevented the oxidation of sulphides on the sea floor.

Non-local drivers of the summer hypoxia in the East China Sea off the Changjiang Estuary

NASA Astrophysics Data System (ADS)

Qian, Wei; Dai, Minhan; Xu, Min; Kao, Shuh-ji; Du, Chuanjun; Liu, Jinwen; Wang, Hongjie; Guo, Liguo; Wang, Lifang

2017-11-01

The East China Sea (ECS) off the Changjiang (Yangtze River) Estuary, located around the near field of the Changjiang plume (CJP) is a hot spot where phytoplankton blooms in the surface water and hypoxias in the subsurface/bottom waters are frequently observed. Based on field observations conducted in summer 2009 and 2011, we examined non-local drivers associated with the initial dissolved oxygen (DO) levels that had significant impact on the development of summer hypoxias in the ECS off the Changjiang Estuary. The bottom water mass therein could be traced isopycnally at 24.2 < σθ < 25.2 back to the vicinity of the Luzon Strait, ∼1300 km upstream, where subsurface Kuroshio water (∼220 m deep with ∼190 μmol DO kg-1) mixed with the South China Sea subsurface water (∼120 m deep with ∼130 μmol DO kg-1). Owing to the difference in DO of these two source water masses, their mixing ratio ultimately determined the initial DO supply to the ECS bottom water that eventually reached the hypoxic zone. This water mass mixture was also subject to biogeochemical alteration during its travel (∼60 days) after it intruded into the ECS at the northeastern tip of Taiwan. Along the pathway of the intruded bottom-hugging water, we found systematic increases in nutrient concentrations and apparent oxygen utilization, or drawdown in DO following Redfield stoichiometry as a result of marine organic matter decomposition. These non-local factors exerted a synergistic control on the initial DO of CJP bottom water promoting hypoxia formation, although the residence time of the CJP bottom water was relatively short (∼11 days). We contend that such far field drivers should be taken into account in order to better predict the future scenarios of coastal hypoxias in the context of global warming.

Potential Environmental Factors Affecting Oil-Degrading Bacterial Populations in Deep and Surface Waters of the Northern Gulf of Mexico

PubMed Central

Liu, Jiqing; Bacosa, Hernando P.; Liu, Zhanfei

2017-01-01

Understanding bacterial community dynamics as a result of an oil spill is important for predicting the fate of oil released to the environment and developing bioremediation strategies in the Gulf of Mexico. In this study, we aimed to elucidate the roles of temperature, water chemistry (nutrients), and initial bacterial community in selecting oil degraders through a series of incubation experiments. Surface (2 m) and bottom (1537 m) waters, collected near the Deepwater Horizon site, were amended with 200 ppm light Louisiana sweet crude oil and bacterial inoculums from surface or bottom water, and incubated at 4 or 24°C for 50 days. Bacterial community and residual oil were analyzed by pyrosequencing and gas chromatography-mass spectrometry (GC-MS), respectively. The results showed that temperature played a key role in selecting oil-degrading bacteria. Incubation at 4°C favored the development of Cycloclasticus, Pseudoalteromonas, Sulfitobacter, and Reinekea, while 24°C incubations enhanced Oleibacter, Thalassobius, Phaeobacter, and Roseobacter. Water chemistry and the initial community also had potential roles in the development of hydrocarbon-degrading bacterial communities. Pseudoalteromonas, Oleibacter, and Winogradskyella developed well in the nutrient-enriched bottom water, while Reinekea and Thalassobius were favored by low-nutrient surface water. We revealed that the combination of 4°C, crude oil and bottom inoculum was a key factor for the growth of Cycloclasticus, while the combination of surface inoculum and bottom water chemistry was important for the growth of Pseudoalteromonas. Moreover, regardless of the source of inoculum, bottom water at 24°C was a favorable condition for Oleibacter. Redundancy analysis further showed that temperature and initial community explained 57 and 19% of the variation observed, while oil and water chemistry contributed 14 and 10%, respectively. Overall, this study revealed the relative roles of temperature, water chemistry, and initial bacterial community in selecting oil degraders and regulating their evolution in the northern Gulf of Mexico. PMID:28119669

The bottom water exchange between the Singapore Strait and the West Johor Strait

NASA Astrophysics Data System (ADS)

Sun, Yunfang; Eltahir, Elfatih; Malanotte-Rizzoli, Paola

2017-08-01

As a part of the border between Singapore and Malaysia, the West Johor Strait (WJS) suffered newly from harmful algal blooms. There is no previous study showing the source of the nutrients in the WJS. This paper is investigating the possible water exchange between the water in the WJS and the bottom water in Singapore Strait. This paper adopts a two-level nesting atmosphere-ocean coupled models to downscale the global atmosphere-ocean model into the Singapore coastal water, keeping the large-scale and long-term ocean and climate circulation signals and the advantages of the high-resolution. Based on the high-resolution ocean circulation fields, a Lagrangian particle tracking model is used to trace the Singapore Strait's bottom water movement and the water mixing in the WJS. The results showed that the numerical models well resolved the Singapore coastal water regional circulation. There is a small but significant bottom water (1.25%) transport from the Singapore Strait to the WJS, which occurs from the southwest coastline of Singapore. The bottom water in the Singapore Strait prefers to enter the WJS during the spring tide and the flood period, and stay in Johor Strait for 6.4 days. The spring tide is the first-order factor for the water vertical mixing in the WJS, the wind is also very important for the vertical mixing especially in neap tide condition. An overall very important factor is the light perturbation. With the strongest vertical mixing of nutrients and bottom sediments due to the spring tide, the latter ones may inhibit the light penetration during the spring tide and reduce the algal bloom. The light penetration otherwise is greater during the neap tide, when the winds are the most important factor and hence favor the algal bloom. With the strongest wind in February and the longest permanence time in June and the sufficient nutrient supply in February and June, the most serious algal blooms may happen in February and June in the WJS.

Potential Environmental Factors Affecting Oil-Degrading Bacterial Populations in Deep and Surface Waters of the Northern Gulf of Mexico.

PubMed

Liu, Jiqing; Bacosa, Hernando P; Liu, Zhanfei

2016-01-01

Understanding bacterial community dynamics as a result of an oil spill is important for predicting the fate of oil released to the environment and developing bioremediation strategies in the Gulf of Mexico. In this study, we aimed to elucidate the roles of temperature, water chemistry (nutrients), and initial bacterial community in selecting oil degraders through a series of incubation experiments. Surface (2 m) and bottom (1537 m) waters, collected near the Deepwater Horizon site, were amended with 200 ppm light Louisiana sweet crude oil and bacterial inoculums from surface or bottom water, and incubated at 4 or 24°C for 50 days. Bacterial community and residual oil were analyzed by pyrosequencing and gas chromatography-mass spectrometry (GC-MS), respectively. The results showed that temperature played a key role in selecting oil-degrading bacteria. Incubation at 4°C favored the development of Cycloclasticus, Pseudoalteromonas , Sulfitobacter , and Reinekea , while 24°C incubations enhanced Oleibacter, Thalassobius, Phaeobacter, and Roseobacter. Water chemistry and the initial community also had potential roles in the development of hydrocarbon-degrading bacterial communities. Pseudoalteromonas , Oleibacter , and Winogradskyella developed well in the nutrient-enriched bottom water, while Reinekea and Thalassobius were favored by low-nutrient surface water. We revealed that the combination of 4°C, crude oil and bottom inoculum was a key factor for the growth of Cycloclasticus , while the combination of surface inoculum and bottom water chemistry was important for the growth of Pseudoalteromonas . Moreover, regardless of the source of inoculum, bottom water at 24°C was a favorable condition for Oleibacter. Redundancy analysis further showed that temperature and initial community explained 57 and 19% of the variation observed, while oil and water chemistry contributed 14 and 10%, respectively. Overall, this study revealed the relative roles of temperature, water chemistry, and initial bacterial community in selecting oil degraders and regulating their evolution in the northern Gulf of Mexico.

Anchoring submersible ultrasonic receivers in river channels with stable substrate

USGS Publications Warehouse

Bettoli, Phillip William; Scholten, G.D.; Hubbs, D.

2010-01-01

We developed an anchoring system for submersible ultrasonic receivers (SURs) that we placed on the bottom of the riverine reaches of three main-stem reservoirs in the upper Tennessee River. Each anchor consisted of a steel tube (8.9 x 35.6 cm) welded vertically to a round plate of steel (5.1 x 40.6 cm). All seven SURs and their 57-kg anchors were successfully deployed and retrieved three times over 547 d by a dive team employing surface air-breathing equipment and a davit-equipped boat. All of the anchors and their SURs remained stationary over two consecutive winters on the hard-bottom, thalweg sites where they were deployed. The SUR and its anchor at the most downriver site experienced flows that exceeded 2,100 m(3)/s and mean water column velocities of about 0.9 m/s.

Millennial Variability of Eastern Equatorial Bottom Water Oxygenation and Atmospheric CO2 over the past 100 kyr

NASA Astrophysics Data System (ADS)

Marcantonio, F.; Loveley, M.; Wisler, M.; Hostak, R.; Hertzberg, J. E.; Schmidt, M. W.; Lyle, M. W.

2017-12-01

Storage of respired carbon in the deep ocean may play a significant role in lowering atmospheric CO2 concentrations by about 80 ppm during the last glacial maximum compared to pre-industrial times. The cause of this sequestration and the subsequent release of the deep respired carbon pool at the last termination remains elusive. Within the last glacial period, on millennial timescales, the relationship between the CO2 cycle and any waxing and waning of a deep respired pool also remains unclear. To further our understanding of the millennial variability in the storage of a deep-ocean respired carbon pool during the last glacial, we measure authigenic uranium and 230Th-derived non-lithogenic barium fluxes (xsBa flux) in two high-sedimentation-rate cores from the Panama Basin of the Eastern Equatorial Pacific (EEP) (8JC, 6° 14.0' N, 86° 02.6' W; 1993 m water depth; 17JC 00° 10.8' S, 85° 52.0' W; 2846 m water depth). Sediment authigenic U concentrations are controlled by the redox state of sediments which, in turn, is a function of the rain of organic material from the surface ocean and the oxygen content of bottom waters. At both 8JC and 17JC, the mismatch between xsBa fluxes, a proxy for the reconstruction of oceanic productivity, and authigenic uranium concentrations suggests that the primary control of the latter values is changes in bottom water oxygenation. Peak authigenic uranium concentrations occur during glacial periods MIS 2, 3, and 4, respectively, and are two to three times higher than those during interglacial periods, MIS 1 and 5. EEP bottom waters were likely suboxic during times of the last glacial period when atmospheric CO2 concentrations were at their lowest concentrations. In addition, the pattern of increased deep-water oxygenation during times of higher CO2 during the last glacial is similar to that reported in a study of authigenic U in sediments from the Antarctic Zone of the Southern Ocean (Jaccard et al., 2016). We suggest that a respired carbon pool existed within a large swath of the abyssal Southern and Pacific Oceans throughout the entire last glacial cycle, and that this respired carbon was periodically released through increased ventilation of deep ocean waters. Jaccard et al. (2016) Nature 530, 207-210.

Physical-property, water-quality, plankton, and bottom-material data for Devils Lake and East Devils Lake, North Dakota, September 1988 through October 1990

USGS Publications Warehouse

Sando, Steven K.; Sether, Bradley A.

1993-01-01

Physical-properties were measured and water-quality, plankton, and bottom-material samples were collected at 10 sites in Devils Lake and East Devils Lake during September 1988 through October 1990 to study water-quality variability and water-quality and plankton relations in Devils Lake and East Devils Lake. Physical properties measured include specific conductance, pH, water temperature, dissolved-oxygen concentration, water transparency, and light transmission. Water-quality samples were analyzed for concentrations of major ions, selected nutrients, and selected trace elements. Plankton samples were examined for identification and enumeration of phytoplankton and zooplankton species, and bottom-material samples were analyzed for concentrations of selected nutrients. Data-collection procedures are discussed and the data are presented in tabular form.

Bottom water circulation in Cascadia Basin

NASA Astrophysics Data System (ADS)

Hautala, Susan L.; Paul Johnson, H.; Hammond, Douglas E.

2009-10-01

A combination of beta spiral and minimum length inverse methods, along with a compilation of historical and recent high-resolution CTD data, are used to produce a quantitative estimate of the subthermocline circulation in Cascadia Basin. Flow in the North Pacific Deep Water, from 900-1900 m, is characterized by a basin-scale anticyclonic gyre. Below 2000 m, two water masses are present within the basin interior, distinguished by different potential temperature-salinity lines. These water masses, referred to as Cascadia Basin Bottom Water (CBBW) and Cascadia Basin Deep Water (CBDW), are separated by a transition zone at about 2400 m depth. Below the depth where it freely communicates with the broader North Pacific, Cascadia Basin is renewed by northward flow through deep gaps in the Blanco Fracture Zone that feeds the lower limb of a vertical circulation cell within the CBBW. Lower CBBW gradually warms and returns to the south at lighter density. Isopycnal layer renewal times, based on combined lateral and diapycnal advective fluxes, increase upwards from the bottom. The densest layer, existing in the southeast quadrant of the basin below ˜2850 m, has an advective flushing time of 0.6 years. The total volume flushing time for the entire CBBW is 2.4 years, corresponding to an average water parcel residence time of 4.7 years. Geothermal heating at the Cascadia Basin seafloor produces a characteristic bottom-intensified temperature anomaly and plays an important role in the conversion of cold bottom water to lighter density within the CBBW. Although covering only about 0.05% of the global seafloor, the combined effects of bottom heat flux and diapycnal mixing within Cascadia Basin provide about 2-3% of the total required global input to the upward branch of the global thermohaline circulation.

The Sinking and Spreading of The Antarctic Deep Ice Shelf Water In The Ross Sea Studied By In Situ Observaions and Numerical Modeling

NASA Astrophysics Data System (ADS)

Rubino, A.; Budillon, G.; Pierini, S.; Spezie, G.

The sinking and spreading of the Deep Ice Shelf Water (DISW) in the Ross Sea are analyzed using in situ observations and the results of a nonlinear, reduced-gravity, frontal layered numerical "plume" model which is able to simulate the motion of a bottom-arrested current over realistic topography. The model is forced by prescribing the thickness of the DISW vein as well as its density structure at the southern model boundary. The ambient temperature and salinity are imposed using hydrographic data acquired by the Italian PNRA-CLIMA project. In the model water of the quiescent ambient ocean is allowed to entrain in the active deep layer due to a simple param- eterization of turbulent mixing. The importance of forcing the model with a realistic ambient density is demonstrated by carrying out a numerical simulation in which the bottom active layer is forced using an idealized ambient density. In a more realis- tic simulation the path and the density structure of the DISW vein flowing over the Challenger Basin are obtained and are found to be in good agreement with data. The evolution of the deep current beyond the continental shelf is also simulated. It provides useful information on the water flow and mixing in a region of the Ross Sea where the paucity of experimental data does not allow for a detailed description of the deep ocean dynamics.

Drivers of deep-water renewal events observed over 13 years in the South Basin of Lake Baikal

NASA Astrophysics Data System (ADS)

Tsimitri, Chrysanthi; Rockel, Burkhardt; Wüest, Alfred; Budnev, Nikolay M.; Sturm, Michael; Schmid, Martin

2015-03-01

Lake Baikal, with a depth of 1637 m, is characterized by deep-water intrusions that bridge the near-surface layer to the hypolimnion. These episodic events transfer heat and oxygen over large vertical scales and maintain the permanent temperature stratified deep-water status of the lake. Here we evaluate a series of intrusion events that reached the bottom of the lake in terms of the stratification and the wind conditions under which they occurred and provide a new insight into the triggering mechanisms. We make use of long-term temperature and current meter data (2000-2013) recorded in the South Basin of the lake combined with wind data produced with a regional downscaling of the global NCEP-RA1 reanalysis product. A total of 13 events were observed during which near-surface cold water reached the bottom of the South Basin at 1350 m depth. We found that the triggering mechanism of the events is related to the time of the year that they take place. We categorized the events in three groups: (1) winter events, observed shortly before the complete ice cover of the lake that are triggered by Ekman coastal downwelling, (2) under-ice events, and (3) spring events, that show no correlation to the wind conditions and are possibly connected to the increased spring outflow of the Selenga River. This article was corrected on 18 MAR 2015. See the end of the full text for details.

Effects of the bottom boundary condition in numerical investigations of dense water cascading on a slope

NASA Astrophysics Data System (ADS)

Berntsen, Jarle; Alendal, Guttorm; Avlesen, Helge; Thiem, Øyvind

2018-05-01

The flow of dense water along continental slopes is considered. There is a large literature on the topic based on observations and laboratory experiments. In addition, there are many analytical and numerical studies of dense water flows. In particular, there is a sequence of numerical investigations using the dynamics of overflow mixing and entrainment (DOME) setup. In these papers, the sensitivity of the solutions to numerical parameters such as grid size and numerical viscosity coefficients and to the choices of methods and models is investigated. In earlier DOME studies, three different bottom boundary conditions and a range of vertical grid sizes are applied. In other parts of the literature on numerical studies of oceanic gravity currents, there are statements that appear to contradict choices made on bottom boundary conditions in some of the DOME papers. In the present study, we therefore address the effects of the bottom boundary condition and vertical resolution in numerical investigations of dense water cascading on a slope. The main finding of the present paper is that it is feasible to capture the bottom Ekman layer dynamics adequately and cost efficiently by using a terrain-following model system using a quadratic drag law with a drag coefficient computed to give near-bottom velocity profiles in agreement with the logarithmic law of the wall. Many studies of dense water flows are performed with a quadratic bottom drag law and a constant drag coefficient. It is shown that when using this bottom boundary condition, Ekman drainage will not be adequately represented. In other studies of gravity flow, a no-slip bottom boundary condition is applied. With no-slip and a very fine resolution near the seabed, the solutions are essentially equal to the solutions obtained with a quadratic drag law and a drag coefficient computed to produce velocity profiles matching the logarithmic law of the wall. However, with coarser resolution near the seabed, there may be a substantial artificial blocking effect when using no-slip.

A Bottom-up Vulnerability Analysis of Water Systems with Decentralized Decision Making and Demographic Shifts- the Case of Jordan.

NASA Astrophysics Data System (ADS)

Lachaut, T.; Yoon, J.; Klassert, C. J. A.; Talozi, S.; Mustafa, D.; Knox, S.; Selby, P. D.; Haddad, Y.; Gorelick, S.; Tilmant, A.

2016-12-01

Probabilistic approaches to uncertainty in water systems management can face challenges of several types: non stationary climate, sudden shocks such as conflict-driven migrations, or the internal complexity and dynamics of large systems. There has been a rising trend in the development of bottom-up methods that place focus on the decision side instead of probability distributions and climate scenarios. These approaches are based on defining acceptability thresholds for the decision makers and considering the entire range of possibilities over which such thresholds are crossed. We aim at improving the knowledge on the applicability and relevance of this approach by enlarging its scope beyond climate uncertainty and single decision makers; thus including demographic shifts, internal system dynamics, and multiple stakeholders at different scales. This vulnerability analysis is part of the Jordan Water Project and makes use of an ambitious multi-agent model developed by its teams with the extensive cooperation of the Ministry of Water and Irrigation of Jordan. The case of Jordan is a relevant example for migration spikes, rapid social changes, resource depletion and climate change impacts. The multi-agent modeling framework used provides a consistent structure to assess the vulnerability of complex water resources systems with distributed acceptability thresholds and stakeholder interaction. A proof of concept and preliminary results are presented for a non-probabilistic vulnerability analysis that involves different types of stakeholders, uncertainties other than climatic and the integration of threshold-based indicators. For each stakeholder (agent) a vulnerability matrix is constructed over a multi-dimensional domain, which includes various hydrologic and/or demographic variables.

Year-round N2O production by benthic NOx reduction in a monomictic south-alpine lake

NASA Astrophysics Data System (ADS)

Freymond, C. V.; Wenk, C. B.; Frame, C. H.; Lehmann, M. F.

2013-12-01

Nitrous oxide (N2O) is a potent greenhouse gas, generated through microbial nitrogen (N) turnover processes, such as nitrification, nitrifier denitrification, and denitrification. Previous studies quantifying natural sources have mainly focused on soils and the ocean, but the potential role of terrestrial water bodies in the global N2O budget has been widely neglected. Furthermore, the biogeochemical controls on the production rates and the microbial pathways that produce benthic N2O in lakes are essentially unknown. In this study, benthic N2O fluxes and the contributions of the microbial pathways that produce N2O were assessed using 15N label flow-through sediment incubations in the eutrophic, monomictic south basin of Lake Lugano in Switzerland. The sediments were a significant source of N2O throughout the year, with production rates ranging between 140 and 2605 nmol N2O h-1 m-2, and the highest observed rates coinciding with periods of water column stratification and stably anoxic conditions in the overlying bottom water. Nitrate (NO3-) reduction via denitrification was found to be the major N2O production pathway in the sediments under both oxygen-depleted and oxygen-replete conditions in the overlying water, while ammonium oxidation did not contribute significantly to the benthic N2O flux. A marked portion (up to 15%) of the total NO3- consumed by denitrification was reduced only to N2O, without complete denitrification to N2. These fluxes were highest when the bottom water had stabilized to a low-oxygen state, in contrast with the notion that stable anoxia is particularly conducive to complete denitrification without accumulation of N2O. This study provides evidence that lake sediments are a significant source of N2O to the overlying water and may produce large N2O fluxes to the atmosphere during seasonal mixing events.

Dynamics of particle export on the Northwest Atlantic margin

NASA Astrophysics Data System (ADS)

Hwang, Jeomshik; Manganini, Steven J.; Montluçon, Daniel B.; Eglinton, Timothy I.

2009-10-01

The Northwest Atlantic margin is characterized by high biological productivity in shelf and slope surface waters. In addition to carbon supply to underlying sediments, the persistent, intermediate depth nepheloid layers emanating from the continental shelves, and bottom nepheloid layers maintained by strong bottom currents associated with the southward flowing Deep Western Boundary Current (DWBC), provide conduits for export of organic carbon over the margin and/or to the interior ocean. As a part of a project to understand dynamics of particulate organic carbon (POC) cycling in this region, we examined the bulk and molecular properties of time-series sediment trap samples obtained at 968 m, 1976 m, and 2938 m depths from a bottom-tethered mooring on the New England slope (water depth, 2988 m). Frequent occurrences of higher fluxes in deep relative to shallower sediment traps and low Δ 14C values of sinking POC together provide strong evidence for significant lateral transport of aged organic matter over the margin. Comparison of biogeochemical properties such as aluminum concentration and flux, and iron concentration between samples intercepted at different depths shows that particles collected by the deepest trap had more complex sources than the shallower ones. These data also suggest that at least two modes of lateral transport exist over the New England margin. Based on radiocarbon mass balance, about 30% (±10%) of sinking POC in all sediment traps is estimated to be derived from lateral transport of resuspended sediment. A strong correlation between Δ 14C values and aluminum concentrations suggests that the aged organic matter is associated with lithogenic particles. Our results suggest that lateral transport of organic matter, particularly that resulting from sediment resuspension, should be considered in addition to vertical supply of organic matter derived from primary production, in order to understand carbon cycling and export over continental margins.

Contourite drift off Madeira Island (Northeast Atlantic) and implications to Cenozoic bottom-current circulation

NASA Astrophysics Data System (ADS)

Roque, Cristina; Hernández-Molina, F. Javier; Madureira, Pedro; Quartau, Rui; Magalhães, Vitor; Carrara, Gabriela; Santos de Campos, Aldino; Brandão, Filipe; Tomás Vázquez, Juan; Somoza, Luis

2017-04-01

During the last decades several works have been carried out on the morphosedimentary processes driven by bottom-currents in several continental margins and abyssal plains worldwide. However these processes still remain poorly understood on deep-water settings and particularly around oceanic islands. This study is focused on the offshore of Madeira Island (Portugal), which is located in the Northeast Atlantic at about 700 km west of NW Africa. The interpretation of a newly acquired dataset, composed of multibeam bathymetry, Parasound echosounder profiles and multichannel seismic reflection profiles, allowed to identify a giant (about 385 km long and over than 175 km wide) plastered contourite drift, called the "Madeira Drift", developing along the lower slope of the Madeira plateau. It formed on top of a major erosional unconformity that truncates the underlying pelagic deposits, which drape over faulted blocks of Cretaceous oceanic crust. The Madeira Drift is composed of three main regional seismic units showing a predominant aggradational stacking pattern, without evidence of major lateral migration thought time. Its internal configuration indicates that it was build-up by a northwards flowing deep bottom current. These characteristics suggests that an almost persistent and stable water mass has been responsible for its edification trough time. While the precise age of this contourite drift is undetermined, some chronostratigraphic constraints can be determined based upon published works regarding seafloor magnetic anomalies (e.g. Bird et al., 2007), DSDP Site 136drilling data (Hayes et al., 1978). Attending to this, we propose that the possible onset of Madeira Drift must have occurred after Late Cretaceous, within the tertiary period, and quite probably in the Late Eocene / Eocene-Oligocene transition. Based on them is commonly accepted that an enhanced proto-Antarctic Bottom Water (AABW) started to circulate at that time we considered this water mass as the best candidate for the build-up of Madeira Drift. Thus, the Madeira drift represents an exceptional sedimentary record in this sector of the Northeast Atlantic for the earliest phases of the proto-AABW water mass circulation. References: Bird, D.E., Hall, S.A., Burke, K., Casey, J.F., Sawyer, D.S. 2007. Early Central Atlantic Ocean seafloor spreading history. Geosphere, 3, 282-298. doi: 10.1130/GES00047.1 Hayes, D.E., Pimm, A.C., Beckmann, J.P., Benson, W.E., Berger, W.H., Roth, P.H., Supko,P.R., von Rad, U. (1978). Initial Reports, Site 136. doi:10.2973/dsdp.proc.14.1972

Prospecting for zones of contaminated ground-water discharge to streams using bottom-sediment gas bubbles

USGS Publications Warehouse

Vroblesky, Don A.; Lorah, Michelle M.

1991-01-01

Decomposition of organic-rich bottom sediment in a tidal creek in Maryland results in production of gas bubbles in the bottom sediment during summer and fall. In areas where volatile organic contaminants discharge from ground water, through the bottom sediment, and into the creek, part of the volatile contamination diffuses into the gas bubbles and is released to the atmosphere by ebullition. Collection and analysis of gas bubbles for their volatile organic contaminant content indicate that relative concentrations of the volatile organic contaminants in the gas bubbles are substantially higher in areas where the same contaminants occur in the ground water that discharges to the streams. Analyses of the bubbles located an area of previously unknown ground-water contamination. The method developed for this study consisted of disturbing the bottom sediment to release gas bubbles, and then capturing the bubbles in a polyethylene bag at the water-column surface. The captured gas was transferred either into sealable polyethylene bags for immediate analysis with a photoionization detector or by syringe to glass tubes containing wires coated with an activated-carbon adsorbent. Relative concentrations were determined by mass spectral analysis for chloroform and trichloroethylene.

77 FR 25693 - Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-01

... permissible methods of taking, other means of effecting the least practicable adverse impact on the species or... available for public comment (see ADDRESSES) for this IHA. L-DEO, with research funding from the U.S... pattern over an ocean bottom instrument in shallow water. This method is neither practical nor valid in...

Benthic foraminiferal assemblages and bottom water evolution off the Portuguese margin since the Middle Pleistocene

NASA Astrophysics Data System (ADS)

Guo, Qimei; Li, Baohua; Kim, Jin-Kyoung

2017-03-01

The upper 250 meter-long sediment core of Site U1391 (1085 m water depth) retrieved from the Portuguese margin in the Northeast Atlantic Ocean was adopted for the benthic foraminiferal analyses to disclose the variations in Mediterranean Outflow Water (MOW) intensity over the last 0.9 Ma. Benthic foraminifera are abundant at this site and mainly composed of the hyaline forms (80%, such as Cibicidoides/Cibicides spp., Globobulimina spp., Bulimina spp., Uvigerina spp., Melonis spp., Sphaeroidina bulloides, Hoeglundina elegans, Gyroidinoides spp., Lenticulina spp. and Planulina ariminensis), while the agglutinated and porcelaneous forms have only 5% and 14.1% on average, respectively. Down-core variations of the benthic foraminifera show glacial-interglacial contrasts, especially those of Lenticulina spp. and Planulina ariminensis, which is also supported by the benthic foraminiferal cluster analysis. During the interglacial periods, the fauna are dominated by Sphaeroidina bulloides, Lenticulina spp., Planulina ariminensis, Dentalina spp., Cibicidoides robertsonianus and the agglutinated forms, while by Cibicidoides pachyderma, Praeglobobulimina ovata, Praeglobobulimina pupoides, Bulimina mexicana, Uvigerina mediterranea, Bolivinita quadrilatera and mililoids during the glacial periods. Benthic foraminiferal faunal data at Site U1391 was detailed analyzed to disclose the bottom water property over the last 0.9 Ma. Variations of the character species or assemblages, such as Planulina ariminensis, and the ;elevated epibenthos; group suggest that the MOW intensity has typical glacial-interglacial cycles, strengthening during the interglacial periods and weakening during the glacial periods, and reaches its peak at MIS 11. The strongest MOW intensity during MIS 11 confirms the climatic influence of waving sea level on the MOW current by its + 20 m high-stand above the present sea level. The agglutinated benthic foraminifera have a significantly positive correlation with the MOW index of ;elevated epibenthos;, which suggests that their abundance can be used to monitor the hydrodynamic conditions of bottom water off the Portuguese margin. Consistent with the MOW intensity, the lower miliolids content implies a lower salinity which supported the stronger vertical density gradient during the interglacial periods in this region; while the glacial ocean has a higher salinity with a weak vertical density gradient/MOW intensity.

Instability of bottom-water redox conditions during accumulation of Quaternary sediment in the Japan Sea

USGS Publications Warehouse

Piper, D.Z.; Isaacs, C.M.

1996-01-01

The concentrations of Cd, Cr, Cu, Mo, Ni, Sb, U, V, and Zn were measured in early Quaternary sediment (1.32 to 1.08 Ma) from the Oki Ridge in the Japan Sea. The elements were partitioned between a detrital fraction, composed of terrigenous and volcaniclastic aluminosilicate debris, and a marine fraction, composed of biogenic and hydrogenous debris derived from seawater. The most important factors controlling minor-element accumulation rates in the marine fraction were (1) primary productivity in the photic zone, which largely controlled the flux of particulate organic-matter-bound minor elements settling through the water column and onto the seafloor, and (2) bottom-water redox, which determined the suite of elements that accumulated directly from seawater. This marine fraction of minor elements on Oki Ridge recorded six periods of high minor-element abundance. Assuming a constant bulk sediment accumulation rate, each period lasted roughly 5,000 to 10,000 years with a 41,000-year cycle. Accumulation rates of individual elements such as Cd, Mo, and U suggest sulfate-reducing conditions were established in the bottom water during the 10,000-year periods; accumulation rates of Cr and V during the intervening periods are indicative of less reducing, denitrifying conditions. Interelement ratios, for example, Cu:Mo, V:Cr, and Sb:Mo, further reflect bottom-water instability, such that bottom-water redox actually varied from sulfate reducing to denitrifying during the periods of highest minor-element accumulation rates; it varied from denitrifying to oxidizing during the intervening periods. Sediment lithology supports these interpretations of the minor-element distributions; the sediment is finely laminated for several of the periods represented by Cd, Mo, and U maxima and weakly laminated to bioturbated for the intervening periods. The geochemistry of this sediment demonstrates the unambiguous signal of Mo, principally, but of several other minor elements as well in recording sulfate-reducing conditions in bottom water. The forcing function that altered their accumulation, that is, that altered primary productivity and bottom water redox conditions, is problematic. Currently held opinion suggests that O2 depletion was most strongly developed during glacial advances. Low sea level during such times is interpreted to have enhanced primary productivity and restricted bottom-water advection.

Connecting the surface to near-shore bottom waters in the California Current ecosystem: a study of Northern California interannual to decadal oceanographic variability

NASA Astrophysics Data System (ADS)

Fish, C.; Hill, T. M.; Davis, C. V.; Lipski, D.; Jahncke, J.

2017-12-01

Elucidating both surface and bottom water ecosystem impacts of temperature change, acidification, and food web disruption are needed to understand anthropogenic processes in the ocean. The Applied California Current Ecosystem Studies (ACCESS) partnership surveys the California Current within the Greater Farallones and Cordell Bank National Marine Sanctuaries three times annually, sampling water column hydrography and discrete water samples from 0 m and 200 m depth at five stations along three primary transects. The transects span the continental shelf with stations as close as 13 km from the coastline to 65 km. This time series extends from 2004 to 2017, integrating information on climate, productivity, zooplankton abundance, oxygenation, and carbonate chemistry. We focus on the interpretation of the 2012-2017 carbonate chemistry data and present both long term trends over the duration of the time series as well as shorter term variability (e.g., ENSO, `warm blob' conditions) to investigate the region's changing oceanographic conditions. For example, we document oscillations in carbonate chemistry, oxygenation, and foraminiferal abundance in concert with interannual oceanographic variability and seasonal (upwelling) cycles. We concentrate on results from near Cordell Bank that potentially impact deep sea coral ecosystems.

Changes in Bottom Water Physical Properties Above the Mid-Atlantic Ridge Flank in the Brazil Basin

NASA Astrophysics Data System (ADS)

Zhao, Jian; Thurnherr, Andreas M.

2018-01-01

Warming of abyssal waters in recent decades has been widely documented around the global ocean. Here repeat hydrographic data collected in 1997 and 2014 near a deep fracture zone canyon in the eastern Brazil Basin are used to quantify the long-term change. Significant changes are found in the Antarctic Bottom Water (AABW) within the canyon. The AABW in 2014 was warmer (0.08 ± 0.06°C), saltier (0.01 ± 0.005), and less dense (0.005 ± 0.004 kg m-3) than in 1997. In contrast, the change in the North Atlantic Deep Water has complicated spatial structure and is almost indistinguishable from zero at 95% confidence. The resulting divergence in vertical displacement of the isopycnals modifies the local density stratification. At its peak, the local squared buoyancy frequency (N2) near the canyon is reduced by about 20% from 1997 to 2014. Similar reduction is found in the basinwide averaged profiles over the Mid-Atlantic Ridge flank along 25°W in years 1989, 2005, and 2014. The observed changes in density stratification have important implications for internal tide generation and dissipation.

Results of the flowmeter-injection test in the Long Valley Exploratory Well (Phase II), Long Valley, California

USGS Publications Warehouse

Morin, R.H.; Sorey, M.L.; Jacobson, R.D.

1993-01-01

Bayboro Harbor and the Port of St. Petersburg, Florida, form a manmade basin adjacent to Tampa Bay that may supply turbid water to the bay and subsequently affect light penetration in water in the bay. To address concerns about the nature and extent of this potential problem, resuspension of bottom sediments, sedimentation, and tributary storm discharge in the basin were studied. Study results indicated that tidal currents, wind waves, and seiche motions do not resuspend bottom sediments. The maneuvering of a cruise ship in the port resuspended bottom sediments, but these sediments settled within 2 hours. Tidal currents and wave action were not large enough o prevent the resuspended sediments from settling in the basin. Analysis of bathymetric surveys of the port made in 1981, 1986, 1987, and 1989 indicates that the cruise ship has deepened the port along its route and that the displaced sediment has been deposited elsewhere within the port. The storm discharge from two tributaries and the effect of tributary storm runoff on the water quality of the harbor were studied during a storm on November 9, 1989. Booker Creek, which drains an urban watershed, was stratified with a thin layer of turbid freshwater flowing into the harbor over a layer of less turbid saltwater. Salt Creek, which primarily drains Lake Maggiore, was only partially stratified and was less turbid. The turbid water from the creeks increased the turbidity only slightly in the harbor, probably because of mixing with less turbid water and particle settling. Thus, the basin provides mixing and settling, which diminish and eliminate the potentially adverse effect on Tampa Bay from tributary storm runoff and large vessel traffic in the basin.

Influence of the hydrodynamic conditions on the accessibility of the demersal species to the deep water trawl fishery off the Balearic Islands (western Mediterranean)

NASA Astrophysics Data System (ADS)

Amores, A.; Rueda, L.; Monserrat, S.; Guijarro, B.; Pasqual, C.; Massutí, E.

2013-12-01

Ocean mean surface vorticity from gridded multi-mission satellite altimetry data was explored in the Western Mediterranean basin for the period 2000-2010, with the aim of comparing its variability with several species of the deep water fishery in the area. Monthly catches per unit of effort (CPUE) of adult red shrimp (Aristeus antennatus), reported in the deep water bottom trawl fishery developed off northern Mallorca Island displayed a good correlation with surface vorticity. This correlation could be explained by assuming that most of the surface vorticity episodes could reach the bottom, increasing the seabed velocities and producing sediment resuspensions, which could affect the near bottom water turbidity. A. antennatus would respond to this increased turbidity by moving downwards to the deeper waters. This massive displacement of red shrimp specimens away from the fishing grounds would consequently decrease their accesibility to fishing exploitation. This relationship between vorticity and catches also holds for other species , considered as by-catch of the deep water fishery in the area. Results appear to support the suggestion that the water turbidity generated by the vorticy episodes is significant enough to affect the dynamics of the demersal species. The way the surface vorticity observed can affect the bottom sediments is also investigated using a year-long moored near-bottom currentmeter and a sediment trap sited in the fishing grounds.

Molybdenum accumulation in Cariaco basin sediment over the past 24 k.y.: A record of water-column anoxia and climate

USGS Publications Warehouse

Dean, W.E.; Piper, D.Z.; Peterson, L.C.

1999-01-01

Molybdenum (Mo) concentrations in a sediment core from the Cariaco basin on the Venezuelan continental shelf can be partitioned between a marine fraction and a terrigenous fraction. The accumulation rate of the marine fraction of Mo increased abruptly 15 000 calendar years ago (15 ka), from 4 ??g ?? cm-2 ?? yr-1, and then decreased abruptly at 9 ka. The accumulation rate remained high throughout this 6 k.y. period, but exhibited maxima at 15-14 and 12.5 ka, corresponding in time to meltwater pulse IA into the Gulf of Mexico and the onset of the Younger Dryas cold event, respectively. The marine fraction of Mo is interpreted in terms of redox conditions of bottom water, as dictated by both the flux of settling organic matter and bottom-water residence time. Correspondence between geochemical extremes in this core with changes in sea level and global climate demonstrates the high degree to which this ocean-margin basin has responded to the paleoceanographic regime throughout the past 24 k.y.

Effects of glacial meltwater inflows and moat freezing on mixing in an ice-covered antarctic lake as interpreted from stable isotope and tritium distributions

USGS Publications Warehouse

Miller, L.G.; Aiken, G.R.

1996-01-01

Perennially ice-covered lakes in the McMurdo Dry Valleys have risen several meters over the past two decades due to climatic warming and increased glacial meltwater inflow. To elucidate the hydrologic responses to changing climate and the effects on lake mixing processes we measured the stable isotope (??18O and ??D) and tritium concentrations of water and ice samples collected in the Lake Fryxell watershed from 1987 through 1990. Stable isotope enrichment resulted from evaporation in stream and moat samples and from sublimation in surface lake-ice samples. Tritium enrichment resulted from exchange with the postnuclear atmosphere in stream and moat samples. Rapid injection of tritiated water into the upper water column of the make and incorporation of this water into the ice cover resulted in uniformly elevated tritium contents (> 3.0 TU) in these reservoirs. Tritium was also present in deep water, suggesting that a component of bottom water was recently at the surface. During summer, melted lake ice and stream water forms the moat. Water excluded from ice formation during fall moat freezing (enriched in solutes and tritium, and depleted in 18O and 2H relative to water below 15-m depth) may sink as density currents to the bottom of the lake. Seasonal lake circulation, in response to climate-driven surface inflow, is therefore responsible for the distribution of both water isotopes and dissolved solutes in Lake Fryxell.

Method of arsenic removal from water

DOEpatents

Gadgil, Ashok

2010-10-26

A method for low-cost arsenic removal from drinking water using chemically prepared bottom ash pre-treated with ferrous sulfate and then sodium hydroxide. Deposits on the surface of particles of bottom ash form of activated iron adsorbent with a high affinity for arsenic. In laboratory tests, a miniscule 5 grams of pre-treated bottom ash was sufficient to remove the arsenic from 2 liters of 2400 ppb (parts per billion) arsenic-laden water to a level below 50 ppb (the present United States Environmental Protection Agency limit). By increasing the amount of pre-treated bottom ash, even lower levels of post-treatment arsenic are expected. It is further expected that this invention supplies a very low-cost solution to arsenic poisoning for large population segments.

Violent storms within the sea: Dense water formation episodes in the Mediterranean.

NASA Astrophysics Data System (ADS)

Salat, J.

2009-09-01

The Mediterranean is a semi enclosed basin which receives surface water from the Atlantic Ocean. Most of this water is returned into the Ocean with higher density, spreading at more than 1000 m depth (the rest is transported by the atmosphere and the rivers to the Ocean surface). In terms of water budget, the Mediterranean is considered an evaporation basin, but the loss of water is neither the only process that increases the water density nor it is a steady or uniform process. The factors affecting the water density, temperature and salinity, are driven by mass and heat exchanges with the atmosphere. Those exchanges may be by direct contact or mediated by the land. Therefore, changes in water density depend on the water circulation and local weather conditions, both with seasonal and geographical constraints. As the compressibility of water is very low, stratification is expected and horizontal motion is the predominant in the sea interior. Among the few processes that may introduce a vertical component in the water motion are surface heat loss or evaporation that increase the surface water density triggering convective cells. Such processes will be enhanced by surface cooling or by dry continental winds, and counterbalanced by rain, river runoff, solar heating and condensation. Therefore dense water formation are more likely to occur when sea surface temperature is higher than the surface air temperature. There are several scales of convective motions in the ocean, starting from the formation of the surface mixed layer during summer, by night cooling, breezes, and occasional wind storms. During autumn and winter, the vertical scale of the mixing is increasing by steps, through wind storms and progressive cooling, to easily reach the bottom over the continental shelves, typically not deeper than 150 m. However, as the Gibraltar sill is relatively shallow (~350 m) in relation to the average Mediterranean basin (2000-3000 m), the stratification of the deeper layers is weak. Therefore, where and when the surface layer becomes well mixed, typically in winter, in the northern regions, conditions are given (pre-conditioning phase) to the occurrence of dense water formation episodes. Those episodes require the participation of strong cold and dry winds which force an intense evaporation. In the NW Mediterranean, such forcing may act over the continental shelves, like that of the Gulf of Lions, or over deep open seas, typically the central part east of Catalonia and south of Provence. Over the shelf, surface water is expected to be fresher because of the runoff (e.g. the Rhône). Along the continental margin the water circulation, geostrophically adapted, is cyclonic and the stratification in the centre is lower, then density reached may be higher in the central part than on the shelf. However, cooling will be more effective over the shelf as the heat content of the water column is lower because it is much shorter. Once density over the shelf is high enough, the bottom water overflows and violently sinks along the slope in relatively narrow areas through what has been called a cascading event. In the central part, dense water formed sinks almost vertically in funnels not larger than a few kilometres in diameter, and is accompanied by a compensating rise of water from great depth on all sides. In such open sea winter convection events, the dense water can sink some 800 m within a matter of hours and may reach the bottom level, >2500 m deep, within a couple of days. Such short and violent episodes, cascading or open sea convection, of a few days' duration supply enough water to feed the lower layer to compensate the outflow through the Strait of Gibraltar for several weeks. The repeated events in some few points across the Mediterranean, like those above mentioned, are maintaining the Mediterranean circulation and the water exchanges with the Ocean. The overall amount of dense water formed however is highly variable from one year to another according to the forcings involved and perturbations of the water circulation.

Primary Production and Respiration in the Louisiana Coastal Current Drive Patterns of Metabolism and Oxygen on the Louisiana Shelf

NASA Astrophysics Data System (ADS)

Lehrter, J. C.; Fung, M.

2017-12-01

Nutrients loads delivered by the Mississippi River to the Louisiana continental shelf (LCS) stimulate phytoplankton production of organic matter and coupled community respiration. These processes ultimately consume oxygen in bottom waters and promote the development of hypoxia and anoxia on the LCS. Several recent studies have emphasized the importance of nearshore (<15 m depth) phytoplankton production and respiration as a principal driver of heterotrophy and oxygen concentration patterns across this shelf. However, no studies to date have measured these nearshore rates. Other studies have invoked a more classical pattern of surface water primary production fueling water-column and bottom water respiration directly beneath through vertical deposition of organic matter. Yet, patterns of heterotrophy that have been observed across most of the LCS do not seem to support this hypothesis. In this study, we investigated these two different ideas by measuring primary production and respiration rates in distinct water masses at stations spanning salinity and depth gradients on the LCS in spring and summer of 2017. Over the course of this study, we have consistently observed highest primary production and respiration rates in nearshore waters of the Louisiana Coastal Current. This narrow band of low salinity water deriving from the Mississippi and Atchafalaya rivers exhibits maximum production rates exceeding 200 mmol C m-3 d-1 and maximum P/R > 10. Other water masses investigated, which included: surface water at offshore locations (> 15 m depth), sub-surface chlorophylla maxima, mid-water O2 minima and maxima, and bottom water, had average production and respiration rates that were 4-10 fold lower than in the nearshore zone and P/R < 1. These results and a scaling analysis demonstrate the potential for organic matter subsidies from the Louisiana Coastal Current to fuel respiration across the wider shelf and downcoast of the river inputs. Further, the results support recent physical and modeling analyses indicating that mid-water O2 minima and maxima observed on the LCS are primarily derived from lateral advection as opposed to developing in place as a result of excess primary production, sinking, and respiration.

Spatial variability of surface-sediment porewater pH and related water-column characteristics in deep waters of the northern South China Sea

NASA Astrophysics Data System (ADS)

Shao, Changgao; Sui, Yi; Tang, Danling; Legendre, Louis

2016-12-01

This study analyzes the pH of surface-sediment porewater (i.e. 2-3 cm below the water-sediment interface), and concentrations of CaCO3 and organic carbon (OC) in 1192 sediment cores from the northern South China Sea, in water depths ranging from 137 to 3702 m. This is the first study in the literature to analyze the large-scale spatial variability of deep-water surface-sediment pH over a large ocean basin. The data showed strong spatial variations in pH. The lowest pH values (<7.3) were observed south of Hainan Island, an area that is affected by summer upwelling and freshwater runoff from the Pearl and Red Rivers. Moderately low pH values (generally 7.3-7.5) occurred in two other areas: a submarine canyon, where sediments originated partly from the Pearl River and correspond to a paleo-delta front during the last glacial period; and southwest of Taiwan Island, where waters are affected by the northern branch of the Kuroshio intrusion current (KIC) and runoff from Taiwan rivers. The surface sediments with the highest pH (⩾7.5, and up to 8.3) were located in a fourth area, which corresponded to the western branch of the KIC where sediments have been intensively eroded by bottom currents. The pH of surface-sediment porewater was significantly linearly related to water depth, bottom-water temperature, and CaCO3 concentration (p < 0.05 for the whole sampling area). This study shows that the pH of surface-sediment porewater can be sensitive to characteristics of the overlying water column, and suggests that it will respond to global warming as changes in surface-ocean temperature and pH progressively reach deeper waters.

Climatic records of the last and penultimate deglaciations in the South Atlantic and South Indian Ocean

NASA Astrophysics Data System (ADS)

Michel, Elisabeth; Waelbroeck, Claire; Govin, Aline; Skinner, Luke; Vàzquez Riveiros, Natalia; Dewilde, Fabien; Isguder, Gulay; Rebaubier, Hélène

2013-04-01

Surface and deep-water records of Termination I and II in two twin South Atlantic deep-sea cores (44°09' S, 14°14' W, 3770 m depth) and one South Indian core (46°29' S, 88°01' E, 3420 m depth) are presented. Sea surface temperature has been reconstructed based on planktonic foraminifera census counts in all cases, as well as Mg/Ca of G. bulloides and N. pachyderma s. over the last deglaciation. The uncertainty on reconstructed SST using different statistical methods and different faunal databases is assessed. Over the last deglaciation, combined 14C dating and correlation of the SST record with the air temperature signal recorded in Antarctic ice cores allowed us to correct for variable surface reservoir ages in the South Atlantic core (Skinner et al., 2010). Preliminary dating of the South Indian core over the last termination has been done by correlation of its magnetic signal with those of a neighboring 14C dated core (Smart et al., 2010). We have refined the later age scale using the Atlantic core age scale as reference. Benthic isotopic signals in the South Atlantic and South Indian cores over the last deglaciation exhibit the same amplitude and timing. Our results thus indicate that bottom waters at the South Indian site remained isolated from better ventilated deep waters of northern origin until ~15 ka (Waelbroeck et al., 2011). Over Termination II, the two cores have been dated by correlation of their SST records with the air temperature signal recorded in EDC versus the EDC3 age scale (Govin et al., 2009; 2012). A careful examination of the various sources of uncertainty on the derived dating has been performed. Benthic and planktonic isotopic signals reveal analogies but also differences with respect to the last termination. SST was significantly warmer during the Last Interglacial than during the Holocene in both sites. South Atlantic deep waters were also significantly better ventilated during the Last Interglacial than during the Holocene, whereas bottom water ventilation was similar during these two interglacials at the South Indian site.

WAVECALC: an Excel-VBA spreadsheet to model the characteristics of fully developed waves and their influence on bottom sediments in different water depths

NASA Astrophysics Data System (ADS)

Le Roux, Jacobus P.; Demirbilek, Zeki; Brodalka, Marysia; Flemming, Burghard W.

2010-10-01

The generation and growth of waves in deep water is controlled by winds blowing over the sea surface. In fully developed sea states, where winds and waves are in equilibrium, wave parameters may be calculated directly from the wind velocity. We provide an Excel spreadsheet to compute the wave period, length, height and celerity, as well as horizontal and vertical particle velocities for any water depth, bottom slope, and distance below the reference water level. The wave profile and propagation can also be visualized for any water depth, modeling the sea surface change from sinusoidal to trochoidal and finally cnoidal profiles into shallow water. Bedload entrainment is estimated under both the wave crest and the trough, using the horizontal water particle velocity at the top of the boundary layer. The calculations are programmed in an Excel file called WAVECALC, which is available online to authorized users. Although many of the recently published formulas are based on theoretical arguments, the values agree well with several existing theories and limited field and laboratory observations. WAVECALC is a user-friendly program intended for sedimentologists, coastal engineers and oceanographers, as well as marine ecologists and biologists. It provides a rapid means to calculate many wave characteristics required in coastal and shallow marine studies, and can also serve as an educational tool.

Pleistocene Thermocline Reconstruction and Oxygen Minimum Zone Evolution in the Maldives

NASA Astrophysics Data System (ADS)

Yu, S. M.; Wright, J.

2017-12-01

Drift deposits of the southern flank the Kardiva Channel in the eastern Inner Sea of the Maldives provide a complete record of Pleistocene water column changes in conjunction with monsoon cyclicity and fluctuations in the current system. We sampled IODP Site 359-U1467 to reconstruct water column using foraminiferal stable isotope records. This unlithified lithostratigraphic unit is rich in well-preserved microfossils and has an average sedimentation rate of 3.4 cm/yr. Marine Isotope Stages 1-6 were identified and show higher sedimentation rates during the interglacial sections approaching 6 cm/kyr. We present the δ13C and δ18O record of planktonic and benthic foraminiferal species taken at intervals of 3 cm. Globigerinoides ruber was used to constrain surface conditions. The thermocline dwelling species, Globorotalia menardii, was chosen to monitor fluctuations in the thermocline compared to the mixed layer. Lastly, the δ13C of the benthic species, Cibicidoides subhaidingerii and Planulina renzi, reveal changes to the bottom water ventilation and expansion of oxygen minimum zones over time. All three taxa recorded similar changes in δ18O over the glacial/interglacial cycles which is remarkable given the large sea level change ( 120 m) and the relatively shallow water depth ( 450 m). There is a small increase in the δ13C gradient during the glacial intervals which might reflect less ventilated bottom waters in the Inner Sea. This multispecies approach allows us to better constrain the thermocline hydrography and suggests that changes in the OMZ thickness are driven by the intensification of the monsoon cycles while painting a more cohesive picture to the changes in the water column structure.

Diel Vertical Dynamics of Gelatinous Zooplankton (Cnidaria, Ctenophora and Thaliacea) in a Subtropical Stratified Ecosystem (South Brazilian Bight)

PubMed Central

Nogueira Júnior, Miodeli; Brandini, Frederico Pereira; Codina, Juan Carlos Ugaz

2015-01-01

The diel vertical dynamics of gelatinous zooplankton in physically stratified conditions over the 100-m isobath (~110 km offshore) in the South Brazilian Bight (26°45’S; 47°33’W) and the relationship to hydrography and food availability were analyzed by sampling every six hours over two consecutive days. Zooplankton samples were taken in three depth strata, following the vertical structure of the water column, with cold waters between 17 and 13.1°C, influenced by the South Atlantic Central Water (SACW) in the lower layer (>70 m); warm (>20°C) Tropical Water in the upper 40 m; and an intermediate thermocline with a deep chlorophyll-a maximum layer (0.3–0.6 mg m-3). Two distinct general patterns were observed, emphasizing the role of (i) physical and (ii) biological processes: (i) a strong influence of the vertical stratification, with most zooplankton absent or little abundant in the lower layer. The influence of the cold SACW on the bottom layer apparently restricted the vertical occupation of most species, which typically inhabit epipelagic warm waters. Even among migratory species, only a few (Aglaura hemistoma, Abylopsis tetragona eudoxids, Beroe sp., Thalia democratica, Salpa fusiformis) crossed the thermocline and reached the bottom layer. (ii) A general tendency of partial migrations, with variable intensity depending on the different species and developmental stages; populations tended to be more widely distributed through the water column during daylight, and to become more aggregated in the upper layer during the night, which can be explained based on the idea of the “hunger-satiation hypothesis”, maximizing feeding and minimizing the chances of being predated. PMID:26637179

Diel Vertical Dynamics of Gelatinous Zooplankton (Cnidaria, Ctenophora and Thaliacea) in a Subtropical Stratified Ecosystem (South Brazilian Bight).

PubMed

Nogueira Júnior, Miodeli; Brandini, Frederico Pereira; Codina, Juan Carlos Ugaz

2015-01-01

The diel vertical dynamics of gelatinous zooplankton in physically stratified conditions over the 100-m isobath (~110 km offshore) in the South Brazilian Bight (26°45'S; 47°33'W) and the relationship to hydrography and food availability were analyzed by sampling every six hours over two consecutive days. Zooplankton samples were taken in three depth strata, following the vertical structure of the water column, with cold waters between 17 and 13.1°C, influenced by the South Atlantic Central Water (SACW) in the lower layer (>70 m); warm (>20°C) Tropical Water in the upper 40 m; and an intermediate thermocline with a deep chlorophyll-a maximum layer (0.3-0.6 mg m-3). Two distinct general patterns were observed, emphasizing the role of (i) physical and (ii) biological processes: (i) a strong influence of the vertical stratification, with most zooplankton absent or little abundant in the lower layer. The influence of the cold SACW on the bottom layer apparently restricted the vertical occupation of most species, which typically inhabit epipelagic warm waters. Even among migratory species, only a few (Aglaura hemistoma, Abylopsis tetragona eudoxids, Beroe sp., Thalia democratica, Salpa fusiformis) crossed the thermocline and reached the bottom layer. (ii) A general tendency of partial migrations, with variable intensity depending on the different species and developmental stages; populations tended to be more widely distributed through the water column during daylight, and to become more aggregated in the upper layer during the night, which can be explained based on the idea of the "hunger-satiation hypothesis", maximizing feeding and minimizing the chances of being predated.

Hydrogeology of the Seldovia area, Alaska

USGS Publications Warehouse

Nelson, Gordon L.; Danskin, Wesley R.

1980-01-01

Surficial materials in the Seldovia area, Alaska, are mapped as glacial drift over sedimentary bedrock, glacial drift over igneous and metamorphic bedrock, valley-bottom, alluvium, alluvial fan deposits, beach and intertidal deposits, and peat. Unconsolidated materials are generally less than 10 feet thick except in well-drained glacial deposits along the Seldovia-Jakolof Bay Road and in depressions in the bedrock surface. These depressions are poorly drained and commonly contain peat bogs. Development of domestic wells (1-15 gallons per minute) may be possible from unconsolidated materials and sedimentary bedrock, but larger water requirements must be met from surface-water sources. In areas having the water table or top of bedrock at shallow depths, effluent from sewage disposal systems may cause pollution of the land surface and nearby surface water. Seepage from hillside aquifers and unstable land along the coast of Kachemak Bay may adversely affect roads and structures. (USGS)

Hydrochemistry of the Tumen River Estuary, Sea of Japan

NASA Astrophysics Data System (ADS)

Tishchenko, P. Ya.; Semkin, P. Yu.; Pavlova, G. Yu.; Tishchenko, P. P.; Lobanov, V. B.; Marjash, A. A.; Mikhailik, T. A.; Sagalaev, S. G.; Sergeev, A. F.; Tibenko, E. Yu.; Khodorenko, N. D.; Chichkin, R. V.; Shvetsova, M. G.; Shkirnikova, E. M.

2018-03-01

The hydrological and hydrochemical parameters of the Tumen River estuary were collected at 13 stations in May and October 2015. Vertical temperature, conductivity, dissolved oxygen, chlorophyll fluorescence, and turbidity profiles were obtained. Water was sampled from the surface and bottom layer. The water samples were analyzed for major ions, pH, salinity, concentrations of dissolved oxygen, major nutrients, dissolved organic carbon, humic matter, and δ18O and δD isotopes. This estuary is attributed to microtidal type with a flushing time of about 10 h. A phytoplakton bloom occurred in the top layer of the estuary. For surface horizons, the hydrochemical parameters show a linear correlation with salinity. In the bottom horizons, all these parameters, except for major ions and δ18O and δD isotopes, reveal substantial nonconservative behavior. The nonconservative behavior of the hydrochemical parameters in the bottom waters was mainly caused by degradation of the phytoplankton biomass at the water/sediment interface. Hypoxic conditions were established in the bottom waters of the estuary in May.

Presence of selected chemicals of emerging concern in water and bottom sediment from the St. Louis River, St. Louis Bay, and Superior Bay, Minnesota and Wisconsin, 2010

USGS Publications Warehouse

Christensen, Victoria G.; Lee, Kathy E.; Kieta, Kristen A.; Elliott, Sarah M.

2012-01-01

The St. Louis Bay of Lake Superior receives substantial urban runoff, wastewater treatment plant effluent, and industrial effluent. In 1987, the International Joint Commission designated the St. Louis Bay portion of the lower St. Louis River as one of the Great Lakes Areas of Concern. Concerns exist about the potential effects of chemicals of emerging concern on aquatic biota because many of these chemicals, including endocrine active chemicals, have been shown to affect the endocrine systems of fish. To determine the occurrence of chemicals of emerging concern in the St. Louis River, the St. Louis Bay, and Superior Bay, the U.S. Geological Survey in cooperation with the Minnesota Pollution Control Agency and the Wisconsin Department of Natural Resources collected water and bottom-sediment samples from 40 sites from August through October 2010. The objectives of this study were to (1) identify the extent to which chemicals of emerging concern, including pharmaceuticals, hormones, and other organic chemicals, occur in the St. Louis River, St. Louis Bay, and Superior Bay, and (2) identify the extent to which the chemicals may have accumulated in bottom sediment of the study area. Samples were analyzed for selected wastewater indicators, hormones, sterols, bisphenol A, and human-health pharmaceuticals. During this study, 33 of 89 chemicals of emerging concern were detected among all water samples collected and 56 of 104 chemicals of emerging concern were detected in bottom-sediment samples. The chemical N,N-diethyl-meta-toluamide (DEET) was the most commonly detected chemical in water samples and 2,6-dimethylnaphthalene was the most commonly detected chemical in bottom-sediment samples. In general, chemicals of emerging concern were detected at a higher frequency in bottom-sediment samples than in water samples. Estrone (a steroid hormone) and hexahydrohexamethyl cyclopentabensopyran (a synthetic fragrance) were the most commonly detected endocrine active chemicals in water samples; beta-sitosterol (a plant sterol), estrone, and 4-tert-octylphenol (an alkylphenol) were the most commonly detected endocrine active chemicals in bottom-sediment samples. The greater detection frequency of chemicals in bottom-sediment samples compared to the detection frequency in water samples indicates that bottom sediment is an important sink for chemicals of emerging concern. At least one polycyclic aromatic hydrocarbon was detected in every sample; and in most samples, all nine polycyclic aromatic hydrocarbons included in analyses were detected. Bottom sediment collected from Superior Bay had the most polycyclic aromatic hydrocarbon detections of the sediment sampling locations.

Acoustic tracking of woodhead seabed drifters

NASA Technical Reports Server (NTRS)

Mayhue, R. J.; Lovelady, R. W.

1977-01-01

An investigation was conducted to determine the feasibility of tracking Woodhead seabed drifters that were instrumented with miniature acoustic transmitters having a range in water in excess of 1.0 n.mi. A trial cruise at the entrance of Delaware Bay, with the R.V. Annandale as the sonar-tracking vessel, verified acoustic communications and positioning of the bottom drifters. A demonstration cruise with the R.V. Annandale was also performed in the New York Bight to attempt to collect information on bottom water movement near the sewage-sluge dump site. Results from the tracking mission in the New York Bight suggested that bottom water currents were negligible near the dump site during the time interval from November 7-12, 1975, and that shipboard sonar tracking of acoustic Woodhead seabed drifters could provide useful Lagragian information on bottom water movement caused by tidal and other nonstorm effects.

Chemical analyses of elutriates, native water, and bottom material from the Chetco, Rogue, and Columbia rivers in western Oregon

USGS Publications Warehouse

Fuhrer, Gregory J.

1984-01-01

Chemical analyses of elutriates, bottom sediment, and water samples for selected metals, nutrients and organic compounds including insecticides, herbicides, and acid/neutral extractables have been made to provide data to determine short-term water-quality conditions associated with dredging operations in rivers and estuaries. Between April and August 1982, data were collected from the Chetco and Rogue River estuaries in southwestern Oregon, and from the mouth of the Columbia River in the northwestern Oregon to Cathlamet Bay, 18.2 miles upstream. In an elutriation test, bottom materials from a potential dredge site are mixed with native water - collected from either a dredge or disposal site - and the liquid portion of the mixture is removed, filtered, and chemically analyzed. Presented in this report are chemical and physical analyses of elutriates, native water, and bottom material for selected metals, ammonia, organic carbon, pesticides, particle size, and gas chromatographic/mass spectrometric semi-quantitative organic scans. Elutriate and bottom-material samples were screened specifically for phenolic compounds, particularly the chlorinated phenols; phenol was the only compound identified. Elutriate-test results showed variability for selected trace-metal concentrations of dissolved chemicals as follows: in micrograms per liter, arsenic ranged from < 1 to 15, cadmium from 1 to 210, copper from < 1 to 13, chromium from < 1 to 5, and nickel from 2 to 18. Results of computations to determine the amount of a constituent associated with bottom material and interstitial water and subsequently released (dissolved) into the elutriate-test native-mixing water are presented for selected trace metals. The highest elutriate-test release was 35 percent for manganese; the second highest, 5 percent for cadmium. All other computed releases were less than or equal to 1 percent. (USGS)

14 CFR 23.533 - Hull and main float bottom pressures.

Code of Federal Regulations, 2011 CFR

2011-01-01

... Water Loads § 23.533 Hull and main float bottom pressures. (a) General. The hull and main float...=seaplane stalling speed (knots) at the design water takeoff weight with flaps extended in the appropriate...) at the design water takeoff weight with flaps extended in the appropriate takeoff position; and β...

14 CFR 23.533 - Hull and main float bottom pressures.

Code of Federal Regulations, 2010 CFR

2010-01-01

... Water Loads § 23.533 Hull and main float bottom pressures. (a) General. The hull and main float...=seaplane stalling speed (knots) at the design water takeoff weight with flaps extended in the appropriate...) at the design water takeoff weight with flaps extended in the appropriate takeoff position; and β...

Sediment Transport over a Dredge Pit, Sandy Point Southeast, west flank of the Mississippi River during Summer Upcoast Currents: a Coupled Wave, Current and Sediment Numerical Model

NASA Astrophysics Data System (ADS)

Chaichitehrani, N.; Li, C.; Xu, K.; Bentley, S. J.; Miner, M. D.

2017-12-01

Sandy Point southeast, an elongated sand resource, was dredged in November 2012 to restore Pelican Island, Louisiana. Hydrodynamics and wave propagation patterns along with fluvial sediments from the Mississippi River influence the sediment and bottom boundary layer dynamics over Sandy Point. A state-of-the-art numerical model, Delft3D, was implemented to investigate current variations and wave transformation on Sandy Point as well as sediment transport pattern. Delft3d FLOW and WAVE modules were coupled and validated using WAVCIS and NDBC data. Sediment transport model was run by introducing both bed and river sediments, consisted of mainly mud and a small fraction of sand. A sediment transport model was evaluated for surface sediment concentration using data derived from satellite images. The model results were used to study sediment dynamics and bottom boundary layer characteristics focused on the Sandy Point area during summer. Two contrasting bathymetric configurations, with and without the Sandy Point dredge pit, were used to conduct an experiment on the sediment and bottom boundary layer dynamics. Preliminary model results showed that the presence of the Sandy Point pit has very limited effect on the hydrodynamics and wave pattern at the pit location. Sediments from the Mississippi River outlets, especially in the vicinity of the pit, get trapped in the pit under the easterly to the northeasterly upcoast current which prevails in August. We also examined the wave-induced sediment reworking and river-borne fluvial sediment over Sandy Point. The effect of wind induced orbital velocity increases the bottom shear stress compared to the time with no waves, relatively small wave heights (lower than 1.5 meters) along the deepest part of the pit (about 20 meters) causes little bottom sediment rework during this period. The results showed that in the summertime, river water is more likely the source of sedimentation in the pit.

Bottom sediments and pore waters near a hydrothermal vent in Lake Baikal (Frolikha Bay)

USGS Publications Warehouse

Granina, L.Z.; Klerkx, J.; Callender, E.; Leermakers, M.; Golobokova, L.P.

2007-01-01

We discuss the redox environments and the compositions of bottom sediments and sedimentary pore waters in the region of a hydrothermal vent in Frolikha Bay, Lake Baikal. According to our results, the submarine vent and its companion nearby spring on land originate from a common source. The most convincing evidence for their relation comes from the proximity of stable oxygen and hydrogen isotope compositions in pore waters and in the spring water. The isotope composition indicates a meteoric origin of pore waters, but their major- and minor-element chemistry bears imprint of deep water which may seep through permeable faulted crust. Although pore waters near the submarine vent have a specific enrichment in major and minor constituents, hydrothermal discharge at the Baikal bottom causes a minor impact on the lake water chemistry, unlike the case of freshwater geothermal lakes in the East-African Rift and North America. ?? 2007.

Shelf-Slope Exchanges near Submarine Canyons in the Southern Mid-Atlantic Bight

NASA Astrophysics Data System (ADS)

Wang, H.; Gong, D.

2016-02-01

Shelf-slope exchange processes are major physical drivers of biological productivity near the shelf-break. Observations from two Slocum ocean gliders in Fall 2013 are used to explore the driving mechanisms of cross-shelf-slope exchanges near Norfolk Canyon and Washington Canyon in the southern Mid-Atlantic Bight. Offshore excursion of bottom "cold pool" water, and shoreward intrusion of slope water at surface layer and thermocline depth occurred during northeasterly along-shelf winds. The saline intrusions of surface slope water resided between the cold pool and surface shelf water, and reached the bottom on the outer and mid-shelf, while the offshore excursion of cold pool water was found between the surface and intermediate slope-water over the canyon. Ekman transport calculation shows wind-driven cross-shelf transport can partially explain this interleaving pattern of intrusions. Scaling analysis of double diffusive processes demonstrate that they also likely played a role in the cross-shelf-slope exchange. A unique canyon upwelling event was captured in and around Washington Canyon during a period of southwesterly along-shelf wind and along-shelf flow to the northeast. The water mass distributions and isopycnal responses in both along-canyon and cross-canyon transects are consistent with scaling analysis and numerical studies of canyon upwelling. Temperature-Salinity properties of water masses in the canyon suggest active mixing between shelf and slope water masses near the canyon head. These results point to the importance of wind, double diffusion, and canyon topography on shelf-slope exchange in the MAB.

Near-shore talik development beneath shallow water in expanding thermokarst lakes, Old Crow Flats, Yukon

NASA Astrophysics Data System (ADS)

Roy-Leveillee, Pascale; Burn, Christopher R.

2017-05-01

It is generally assumed that permafrost is preserved beneath shallow lakes and ponds in the Western North American Arctic where water depth is less than about two thirds of the late-winter lake ice thickness. Here we present field observations of talik development beneath water as shallow as 0.2 m despite a lake ice thickness of 1.5 m, in Old Crow Flats (OCF), YT. Conditions leading to the initiation and development of taliks beneath shallow water were investigated with field measurements of shore erosion rates, bathymetry, ice thickness, snow accumulation, and lake bottom temperature near the shores of two expanding lakes in OCF. The sensitivity of talik development to variations in lake bottom thermal regime was then investigated numerically. Where ice reached the lake bottom, talik development was controlled by the ratio of freezing degree days to thawing degree days at the lake bottom (FDDlb/TDDlb). In some cases, spatial variations in on-ice snow depth had a minimal effect on annual mean lake bottom temperature (Tlb) but caused sufficient variations in FDDlb/TDDlb to influence talik development. Where Tlb was close to but greater than 0°C simulations indicated that the thermal offset allowed permafrost aggradation to occur under certain conditions, resulting in irregular near-shore talik geometries. The results highlight the sensitivity of permafrost to small changes in lake bottom thermal conditions where the water column freezes through in early winter and indicate the occurrence of permafrost degradation beneath very shallow water in the near-shore zone of Arctic ponds and lakes.

Mean Lagrangian drift in continental shelf waves

NASA Astrophysics Data System (ADS)

Drivdal, M.; Weber, J. E. H.

2012-04-01

The time- and depth-averaged mean drift induced by barotropic continental shelf waves (CSW's) is studied theoretically for idealized shelf topography by calculating the mean volume fluxes to second order in wave amplitude. The waves suffer weak spatial damping due to bottom friction, which leads to radiation stress forcing of the mean fluxes. In terms of the total wave energy density E¯ over the shelf region, the radiation stress tensor component S¯11 for CSW's is found to be different from that of shallow water surface waves in a non-rotating ocean. For CSW's, the ratio ¯S11/¯E depends strongly on the wave number. The mean Lagrangian flow forced by the radiation stress can be subdivided into a Stokes drift and a mean Eulerian drift current. The magnitude of the latter depends on the ratio between the radiation stress and the bottom stress acting on the mean flow. When the effect of bottom friction acts equally strong on the waves and the mean current, calculations for short CSW's show that the Stokes drift and the friction-dependent wave-induced mean Eulerian current varies approximately in anti-phase over the shelf, and that the latter is numerically the largest. For long CSW's they are approximately in phase. In both cases the mean Lagrangian current, which is responsible for the net particle drift, has its largest numerical value at the coast on the shallow part of the shelf. Enhancing the effect of bottom friction on the Eulerian mean flow, results in a general current speed reduction, as well as a change in spatial structure for long waves. Applying realistic physical parameters for the continental shelf west of Norway, calculations yield along-shelf mean drift velocities for short CSW's that may be important for the transport of biological material, neutral tracers, and underwater plumes of dissolved oil from deep water drilling accidents.

Distribution of green algal mats throughout shallow soft bottoms of the Swedish Skagerrak archipelago in relation to nutrient sources and wave exposure

NASA Astrophysics Data System (ADS)

Pihl, Leif; Svenson, Anders; Moksnes, Per-Olav; Wennhage, Håkan

1999-06-01

Distribution and biomass of green algal mats were studied in marine shallow (0-1 m) soft-bottom areas on the Swedish west coast from 1994 to 1996, by combining aerial photography surveys with ground truth sampling. Filamentous green algae, dominated by species of the genera Cladophora and Enteromorpha, were generally present throughout the study area during July and August, and largely absent in late April and early May. These algae occurred at 60 to 90% of the locations investigated during the summer, and were estimated to cover between 30 and 50% of the total area of shallow soft bottoms of the Swedish Skagerrak archipelago. The distributional patterns were similar during the three years of the investigation and appeared unrelated to annual local nutrient inputs from point sources and river discharge. We postulate that the apparent lack of such a relationship is due to an altered state of nutrient dynamics throughout the archipelago. Mechanisms are likely to involve long-term, diffuse elevations in nutrient levels in coastal waters of the Skagerrak and the Kattegat over several decades leading to current eutrophic conditions, exceeding nutrient requirements for abundant filamentous algal growth. Patterns of algal abundance in our study were largely related to physical factors such as exposure to wind, waves and water exchange under conditions where nutrient loads among embayments seemed to be unlimited. Further, our results show that sediments covered by algal mats had higher carbon and nitrogen contents than unvegetated sediments. We hypothesise that sustained high nutrient loads, manifested in extensive biomass of filamentous algae during summer months, are re-mineralised via decay and sedimentation in the benthic realm. Hence, accumulated carbon and nutrients in the sediment could, in turn, constitute the basic pool for future algal mat production overlying soft bottoms in areas where tidal exchange is limited.

Benthic foraminiferal trace metal uptake: a field calibration from the Arabia Sea Oxygen Minimum Zone

NASA Astrophysics Data System (ADS)

Koho, K. A.; Reichart, G.-J.

2012-04-01

The Arabian Sea Oxygen Minimum Zone (OMZ) is sustained by high surface water productivity and relatively weak mid-depth water column ventilation. High primary productivity drives high respiration rates in the water column, causing severe oxygen depletion between ±150-1400 m water depths, with the oxygen concentrations falling below 2 μM in the core of the OMZ. Living (rose Bengal stained) benthic foraminifera were collected at 10-stations, covering a large bottom water oxygen concentration gradient from the Murray Ridge. This sub-marine ridge is located in the open marine environment of the Arabian Sea and thus not affected by large gradients in surface water productivity such as encountered at the continental margins. Since these sites thus receive similar organic fluxes, but are bathed in bottom waters with contrasting oxygen concentrations, pore water profiles mainly reflect bottom water oxygenation. The study sites represent a natural laboratory to investigate the impact of bottom water chemistry on trace metal incorporation in benthic foraminifera. Trace metal analyses by laser ablation ICP-MS allows detailed single chamber measurements of trace metal content, which can be related to in situ pore water geochemistry. Focus of this study is on redox sensitive trace metal (e.g. Mn, U) incorporation into foraminiferal test calcite in relation to pore water oxygen and carbonate chemistry.

FLUID MODERATED REACTOR

DOEpatents

Wigner, E.P.; Ohlinger, L.A.; Young, G.J.; Weinberg, A.M.

1957-10-22

A reactor which utilizes fissionable fuel elements in rod form immersed in a moderator or heavy water and a means of circulating the heavy water so that it may also function as a coolant to remove the heat generated by the fission of the fuel are described. In this design, the clad fuel elements are held in vertical tubes immersed in heavy water in a tank. The water is circulated in a closed system by entering near the tops of the tubes, passing downward through the tubes over the fuel elements and out into the tank, where it is drawn off at the bottom, passed through heat exchangers to give up its heat and then returned to the tops of the tubes for recirculation.

Sedimentology, CSFe relationships and stable isotopic compositions in Devonian black mudrocks, Mackenzie Mountains, Northwest Territories, Canada

NASA Astrophysics Data System (ADS)

Al-Aasm, I. S.; Morad, S.; Durocher, S.; Muir, I.

1996-11-01

An integrated approach combining CSFe relationships, stable isotopic compositions, and lithofacies characterization was utilized to constrain the palaeoenvironmental and early diagenetic conditions of Middle-Upper Devonian (Eifelian-Frasnian) mudrocks from the Mackenzie Mountains, Northwest Territories, Canada. These rocks include the Hare Indian Formation (informally subdivided into the lower Bluefish Member and the Hare Indian Upper Member), Carcajou Marker and Canol Formation. The Bluefish Member is dominated by black, laminated, organic-rich shales (TOC = 0.35-10.34 wt.%; av. 5.83 wt.) with moderate degrees of pyritization (DOP) of 0.34-0.67 (av. 0.55). These mudrocks were deposited in dysoxic marine bottom-waters that became progressively more oxygenated with time. Variations in TOC, DOP and organic matter δ 13C PDB values (-29.7% to -19.9%; av. -27.2%) are attributed to repeated clastic dilution and increased input of terrestrial organic matter in association with shallowing-upward ramp-clinothem cycles. Pyrite δ 34S CDT values (-32.7% to -18.8%; av. -24.9%) indicate an open system, bacteriogenic seawater-sulphate reduction. Conversely, the overlying Hare Indian Upper Member, characterized by clinothem facies, is composed of grey to green mudstone with minor argillaceous limestones and considerably less organic matter contents (TOC = 0.28-2.99 wt.%; δ 13C = -29.5% to -22.5%). Deposition occurred in oxic to slightly dysoxic waters (DOP = 0.20-0.54; δ 34S = -23.0% to -20.9%), depending on the palaeotopographic location along the depositional slope. A rapid rise in sea level drowned the carbonate 'ramp' member of the Ramparts Formation and produced the thin, organic-rich Carcajou Marker. Bottom-water stagnation that resulted from subdued ramp palaeotopography produced anoxic sea bottom. Black, laminated, organic-rich shales from the Canol Formation (TOC = 1.37-6.68 wt.%) are very similar to those of the Bluefish Member, and are likewise basinal sediments. However, TOC, DOP and organic-matter δ 13C PDB values (-29.1% to -20.8%; av. -26.2%) do not show pronounced variations and indicate that low-energy, quietwater conditions persisted over relatively long, uninterrupted periods of time. High DOP values (0.72-0.93) throughout the Canol Formation suggest that deposition occurred in anoxic bottom-waters, but as basin-fill conditions continued there was a shift to a dysoxic environment (DOP = 0.55-0.65), which grades into nearshore and offshore sequences of the overlying Imperial Formation. In contrast with the Hare Indian Formation, much heavier δ 34S CDT values of pyrite in Canol mudrocks (-11.1% to +5.3%; av. -3.1%) point to bacterial sulphate reduction in a closed to semi-closed system with respect to seawater sulphate.

Development of a GPS buoy system for monitoring tsunami, sea waves, ocean bottom crustal deformation and atmospheric water vapor

NASA Astrophysics Data System (ADS)

Kato, Teruyuki; Terada, Yukihiro; Nagai, Toshihiko; Koshimura, Shun'ichi

2010-05-01

We have developed a GPS buoy system for monitoring tsunami for over 12 years. The idea was that a buoy equipped with a GPS antenna and placed offshore may be an effective way of monitoring tsunami before its arrival to the coast and to give warning to the coastal residents. The key technology for the system is real-time kinematic (RTK) GPS technology. We have successfully developed the system; we have detected tsunamis of about 10cm in height for three large earthquakes, namely, the 23 June 2001 Peru earthquake (Mw8.4), the 26 September 2003 Tokachi earthquake (Mw8.3) and the 5 September 2004 earthquake (Mw7.4). The developed GPS buoy system is also capable of monitoring sea waves that are mainly caused by winds. Only the difference between tsunami and sea waves is their frequency range and can be segregated each other by a simple filtering technique. Given the success of GPS buoy experiments, the system has been adopted as a part of the Nationwide Ocean Wave information system for Port and HArborS (NOWPHAS) by the Ministry of Land, Infrastructure, Transport and Tourism of Japan. They have established more than eight GPS buoys along the Japanese coasts and the system has been operated by the Port and Airport Research Institute. As a future scope, we are now planning to implement some other additional facilities for the GPS buoy system. The first application is a so-called GPS/Acoustic system for monitoring ocean bottom crustal deformation. The system requires acoustic waves to detect ocean bottom reference position, which is the geometrical center of an array of transponders, by measuring distances between a position at the sea surface (vessel) and ocean bottom equipments to return the received sonic wave. The position of the vessel is measured using GPS. The system was first proposed by a research group at the Scripps Institution of Oceanography in early 1980's. The system was extensively developed by Japanese researchers and is now capable of detecting ocean bottom positions with a few centimeters in accuracy. The system is now operational for more than ten sites along the Japanese coasts. Currently, however, the measurements are not continuous but have been done once to several times a year using a boat. If a GPS and acoustic system is placed on a buoy, ocean bottom position could be monitored in near real-time and continuous manner. This will allow us to monitor more detailed and short term crustal deformations at the sea bottom. Another application plan is for an atmospheric research. Previous researchers have shown that GPS is capable of measuring atmospheric water vapor through estimating tropospheric zenith delay measurements of GPS at the sea surface. Information of water vapor content and its temporal variation over sea surface will much contribute to weather forecast on land which has mostly been conducted only by land observations. Considering that the atmospheric mass moves from west to east in general in and around Japanese islands, information of water vapor together with other atmospheric data from an array of GPS buoy placed in the west of Japanese Islands, will much improve weather forecast. We try to examine if this is also feasible. As a conclusion of a series of GPS buoy experiments, we could assert that GPS buoy system will be a powerful tool to monitor ocean surface and much contribute to provide safe and secure life of people.

Shallow water bathymetry correction using sea bottom classification with multispectral satellite imagery

NASA Astrophysics Data System (ADS)

Kazama, Yoriko; Yamamoto, Tomonori

2017-10-01

Bathymetry at shallow water especially shallower than 15m is an important area for environmental monitoring and national defense. Because the depth of shallow water is changeable by the sediment deposition and the ocean waves, the periodic monitoring at shoe area is needed. Utilization of satellite images are well matched for widely and repeatedly monitoring at sea area. Sea bottom terrain model using by remote sensing data have been developed and these methods based on the radiative transfer model of the sun irradiance which is affected by the atmosphere, water, and sea bottom. We adopted that general method of the sea depth extraction to the satellite imagery, WorldView-2; which has very fine spatial resolution (50cm/pix) and eight bands at visible to near-infrared wavelengths. From high-spatial resolution satellite images, there is possibility to know the coral reefs and the rock area's detail terrain model which offers important information for the amphibious landing. In addition, the WorldView-2 satellite sensor has the band at near the ultraviolet wavelength that is transmitted through the water. On the other hand, the previous study showed that the estimation error by the satellite imagery was related to the sea bottom materials such as sand, coral reef, sea alga, and rocks. Therefore, in this study, we focused on sea bottom materials, and tried to improve the depth estimation accuracy. First, we classified the sea bottom materials by the SVM method, which used the depth data acquired by multi-beam sonar as supervised data. Then correction values in the depth estimation equation were calculated applying the classification results. As a result, the classification accuracy of sea bottom materials was 93%, and the depth estimation error using the correction by the classification result was within 1.2m.

Hydrologic and geochemical effects on oxygen uptake in bottom sediments of an effluent-dominated river

USGS Publications Warehouse

McMahon, P.B.; Tindall, J.A.; Collins, J.A.; Lull, K.J.; Nuttle, J.R.

1995-01-01

More than 95% of the water in the South Platte River downstream from the largest wastewater treatment plant serving the metropolitan Denver, Colorado, area consists of treated effluent during some periods of low flow. Fluctuations in effluent-discharge rates caused daily changes in river stage that promoted exchange of water between the river and bottom sediments. Groundwater discharge measurements indicated fluxes of water across the sediment-water interface as high as 18 m3 s−1 km−1. Laboratory experiments indicated that downward movement of surface water through bottom sediments at velocities comparable to those measured in the field (median rate ≈0.005 cm s−1) substantially increased dissolved oxygen uptake rates in bottom sediments (maximum rate 212 ± 10 μmol O2 L−1 h−1) compared with rates obtained when no vertical advective flux was generated (maximum rate 25 ± 8.8 μmol O2 L−1 h−1). Additions of dissolved ammonium to surface waters generally increased dissolved oxygen uptake rates relative to rates measured in experiments without ammonium. However, the magnitude of the advective flux through bottom sediments had a greater effect on dissolved oxygen uptake rates than did the availability of ammonium. Results from this study indicated that efforts to improve dissolved oxygen dynamics in effluent-dominated rivers might include stabilizing daily fluctuations in river stage.

Novel two-way artificial boundary condition for 2D vertical water wave propagation modelled with Radial-Basis-Function Collocation Method

NASA Astrophysics Data System (ADS)

Mueller, A.

2018-04-01

A new transparent artificial boundary condition for the two-dimensional (vertical) (2DV) free surface water wave propagation modelled using the meshless Radial-Basis-Function Collocation Method (RBFCM) as boundary-only solution is derived. The two-way artificial boundary condition (2wABC) works as pure incidence, pure radiation and as combined incidence/radiation BC. In this work the 2wABC is applied to harmonic linear water waves; its performance is tested against the analytical solution for wave propagation over horizontal sea bottom, standing and partially standing wave as well as wave interference of waves with different periods.

Remote Sensing of Suspended Sediments and Shallow Coastal Waters

NASA Technical Reports Server (NTRS)

Li, Rong-Rong; Kaufman, Yoram J.; Gao, Bo-Cai; Davis, Curtiss O.

2002-01-01

Ocean color sensors were designed mainly for remote sensing of chlorophyll concentrations over the clear open oceanic areas (case 1 water) using channels between 0.4 and 0.86 micrometers. The Moderate Resolution Imaging Spectroradiometer (MODIS) launched on the NASA Terra and Aqua Spacecrafts is equipped with narrow channels located within a wider wavelength range between 0.4 and 2.5 micrometers for a variety of remote sensing applications. The wide spectral range can provide improved capabilities for remote sensing of the more complex and turbid coastal waters (case 2 water) and for improved atmospheric corrections for Ocean scenes. In this article, we describe an empirical algorithm that uses this wide spectral range to identifying areas with suspended sediments in turbid waters and shallow waters with bottom reflections. The algorithm takes advantage of the strong water absorption at wavelengths longer than 1 micrometer that does not allow illumination of sediments in the water or a shallow ocean floor. MODIS data acquired over the east coast of China, west coast of Africa, Arabian Sea, Mississippi Delta, and west coast of Florida are used in this study.

Distribution of Different Biogeographical Tintinnids in Yellow Sea and Bohai Sea

NASA Astrophysics Data System (ADS)

Chen, Xue; Li, Haibo; Zhao, Yuan; Zhao, Li; Dong, Yi; Zhang, Wuchang; Xiao, Tian

2018-04-01

There were different biogeographical tintinnids in the oceans. Knowledge of their distribution pattern and mixing was important to the understanding of ecosystem functions. Yellow Sea (YS) and Bohai Sea (BS) were semi-enclosed seas influenced by warm water intrusion and YS cold bottom water. The occurrence of tintinnids in YS and BS during two cruises (summer and winter) were investigated to find out: i) whether warm-water tintinnids appeared in YS and BS; ii) whether boreal tintinnids appeared in high summer; iii) the core area of neritic tintinnids and iv) how these different biogeographical tintinnids mixed. Our results showed that tintinnid community was dominated by neritic tintinnid. We confirmed the occurrence of warm-water tintinnids in summer and winter. In summer, they intruded into BS and mainly distributed in the upper 20 m where Yellow Sea Surface Warm Water (YSSWW) developed. In winter, they were limited in the surface water of central deep region (bottom depth >50 m) of YS where were affected by Yellow Sea Warm Water (YSWW). Boreal tintinnids occurred in YS in high summer (August) and in winter, while they were not observed in BS. In summer, the highest abundance of boreal tintinnids occurred in Yellow Sea Bottom Cold Water, indicating the presence of an oversummering stock. In winter, they were concentrated in the north of YSWW. Vertically, neritic tintinnids abundance was high in the bottom layers. Horizontally, high neritic tintinnids abundance in bottom layers occurred along the 50 m isobath coinciding with the position of front systems. Front systems were the core distribution area of neritic tintinnids. High abundance areas of warm-water and boreal tintinnids were clearly separated vertically in summer, and horizontally in winter. High abundance of neritic tintinnids rarely overlapped with that of warm-water or boreal tintinnids.

33 CFR Schedule II to Subpart A of... - Table of Speeds 1

Code of Federal Regulations, 2011 CFR

2011-07-01

... 33 Navigation and Navigable Waters 3 2011-07-01 2011-07-01 false Table of Speeds 1 II Schedule II... Schedule II to Subpart A of Part 401—Table of Speeds 1 From— To— Maximum speed over the bottom, knots Col.... All other canals 6 6. 1 Maximum speeds at which a vessel may travel in identified areas in both normal...

33 CFR Schedule II to Subpart A of... - Table of Speeds 1

Code of Federal Regulations, 2010 CFR

2010-07-01

... 33 Navigation and Navigable Waters 3 2010-07-01 2010-07-01 false Table of Speeds 1 II Schedule II... Schedule II to Subpart A of Part 401—Table of Speeds 1 From— To— Maximum speed over the bottom, knots Col.... All other canals 6 6. 1 Maximum speeds at which a vessel may travel in identified areas in both normal...

`Log-Chipper' Turbulence in the Convective Boundary Layer.

NASA Astrophysics Data System (ADS)

Kimmel, Shari J.; Wyngaard, John C.; Otte, Martin J.

2002-03-01

Turbulent fluctuations of a conservative scalar in the atmospheric boundary layer (ABL) can be generated by a scalar flux at the surface, a scalar flux of entrainment at the ABL top, and the `chewing up' of scalar variations on the mesoscale. The first two have been previously studied, while the third is examined in this paper through large-eddy simulation (LES). The LES results show that the scalar fluctuations due to the breakdown of mesoscale variations in advected conservative scalar fields, which the authors call the `log-chipper' component of scalar fluctuations, are uniformly distributed through the depth of the convective ABL, unlike the top-down and bottom-up components.A similarity function, similar to those for the top-down and bottom-up scalars, is derived for the log-chipper scalar variance in the convective ABL and used to compare the relative importance of these three processes for generating scalar fluctuations. Representative mesoscale gradients for water vapor mixing ratio and potential temperature are computed from airplane measurements over both land and water. In situations where the entrainment and surface fluxes are sufficiently small, or the ABL depth, turbulence intensity, or the mesoscale scalar gradient is sufficiently large, the variance of the log-chipper scalar fluctuations in mid-ABL can be of the order of the variance of top-down and bottom-up scalars.

Multidecadal warming of Antarctic waters.

PubMed

Schmidtko, Sunke; Heywood, Karen J; Thompson, Andrew F; Aoki, Shigeru

2014-12-05

Decadal trends in the properties of seawater adjacent to Antarctica are poorly known, and the mechanisms responsible for such changes are uncertain. Antarctic ice sheet mass loss is largely driven by ice shelf basal melt, which is influenced by ocean-ice interactions and has been correlated with Antarctic Continental Shelf Bottom Water (ASBW) temperature. We document the spatial distribution of long-term large-scale trends in temperature, salinity, and core depth over the Antarctic continental shelf and slope. Warming at the seabed in the Bellingshausen and Amundsen seas is linked to increased heat content and to a shoaling of the mid-depth temperature maximum over the continental slope, allowing warmer, saltier water greater access to the shelf in recent years. Regions of ASBW warming are those exhibiting increased ice shelf melt. Copyright © 2014, American Association for the Advancement of Science.

Anoxic monimolimnia: Nutrients devious feeders or bombs ready to explode?

NASA Astrophysics Data System (ADS)

Gianni, Areti; Zacharias, Ierotheos

2015-04-01

Coastal regions are under strong human influence and its environmental impact is reflected into their water quality. Oligotrophic estuaries and coastal systems have changed in mesotrophic and/or eutrophic, shown an increase in toxic algal blooms, hypoxic/anoxic events, and massive mortalities of many aquatic and benthic organisms. In strongly stratified and productive water basins, bottom water dissolved oxygen is depleted due to the excessive organic matter decomposition in these depths. Distribution and recycling of nutrients in their water column is inextricably dependent on oxygenation and redox conditions. Bottom water anoxia accelerates PO43-, NH4+ and H2S recycling and accumulation from organic matter decomposition. The anoxic, H2S, PO43- and NH4+ rich bottom water constitutes a toxic layer, threatening the balance of the entire ecosystem. In permanently stratified water basins, storm events could result in stratification destruction and water column total mixing. The turnover brings large amounts of H2S to the surface resulting in low levels of oxygen and massive fish kills. PO43- and NH4+ are released to the interface and surface waters promoting algal blooms. Μore organic matter is produced fueling anoxia. The arising question is, whether the balance of an anoxic water ecosystem is under the threat of its hypolimnetic nutrient and sulfide load, only in the case of storm events and water column total mixing. In polymictic water basins it is clear that the accumulated, in the bottom layer, nutrients will supply surface waters, after the pycnocline overturn. Besides this mechanism of basins' water quality degradation is nowadays recognized as one of the biggest obstacles in eutrophic environments management and restoration efforts. The role of internal load, in permanently stratified water basins, is not so clear. In the present study the impact of storm events on water column stability and bottom water anoxia of meromictic coastal basins, is investigated. The importance of internal load is emerged, presenting the disturbance on the main nutrients, dissolved oxygen, hydrogen sulfide and chlorophyll distribution, caused by the total water column mixing. Additionally, the relationship between temporal nutrients variations in surface layers, of permanent anoxic coastal basins with a) changes on the physicochemical characteristics of their water column, b) changes on the bottom water phosphorus and nitrogen concentration and c) their effect on the basin's primary productivity, is sought. In order to achieve the objectives of this study, two different sets of Aitoliko basin's (western Greece) data were used. The first one includes measurements of physicochemical parameters, nutrients, chlorophyll and hydrogen sulfide, four days after a storm event and the consequent anoxic crisis in Aitoliko basin on 4th of December 2008. The second one contains respective data obtained from a biennial (May 2006-May 2008) basin's monitoring. The changes in the physical, chemical and biological characteristics, of Aitoliko basin water column, after its total mixing, highlighted the importance of the accumulated nutrients and sulfides in the bottom layer. In addition, turned out that bottom layer can supply with nutrients the surface waters, even during periods of high water column stratification. Small scale, subtle, changes in physicochemical and hydrological basin's characteristics promoted this supply, affecting both quantitative and qualitative the ecosystem's primary productivity and shifting its quality character.

CloudSat First Image of a Warm Front Storm Over the Norwegian Sea

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] Figure 1

CloudSat's first image, of a warm front storm over the Norwegian Sea, was obtained on May 20, 2006. In this horizontal cross-section of clouds, warm air is seen rising over colder air as the satellite travels from right to left. The red colors are indicative of highly reflective particles such as water droplets (or rain) or larger ice crystals (or snow), while the blue indicates thinner clouds (such as cirrus). The flat green/blue lines across the bottom represent the ground signal. The vertical scale on the CloudSat Cloud Profiling Radar image is approximately 30 kilometers (19 miles). The blue line below the Cloud Profiling Radar image indicates that the data were taken over water. The inset image shows the CloudSat track relative to a Moderate Resolution Imaging Spectroradiometer (MODIS) infrared image taken at nearly the same time.

Authigenic molybdenum formation in marine sediments: A link to pore water sulfide in the Santa Barbara Basin

USGS Publications Warehouse

Zheng, Yen; Anderson, Robert F.; VanGeen, A.; Kuwabara, J.

2000-01-01

Pore water and sediment Mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the Santa Barbara Basin to examine the connection between authigenic Mo formation and pore water sulfide concentration. Only at the deepest site (580 m), where pore water sulfide concentrations rise to >0.1 ??M right below the sediment water interface, was there active authigenic Mo formation. At shallower sites (550,430, and 340 m), where pore water sulfide concentrations were consistently <0.05 ??M, Mo precipitation was not occuring at the time of sampling. A sulfide concentration of ???0.1 ??M appears to be a threshold for the onset of Mo-Fe-S co-precipitation. A second threshold sulfide concentration of ???100 ??M is required for Mo precipitation without Fe, possibly as Mo-S or as particle-bound Mo. Mass budgets for Mo were constructed by combining pore water and sediment results for Mo with analyses of sediment trap material from Santa Barbara Basin as well as sediment accumulation rates derived from 210Pb. The calculations show that most of the authigenic Mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters. There is, however, a non-lithogenic particulate Mo associated with sinking particles that contributes ???15% to the total authigenic Mo accumulation. Analysis of sediment trap samples and supernant brine solutions indicates the presence of non-lithogenic particulate Mo, a large fraction of which is easily remobilized and, perhaps, associated with Mn-oxides. Our observations show that even with the very high flux of organic carbon reaching the sediment of Santa Barbara Basin, active formation of sedimentary authigenic Mo requires a bottom water oxygen concentration below 3 ??M. However, small but measurable rates of authigenic Mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 ??M, indicating that the formation of authigenic Mo occured in the recent past, but not at the time of sampling. Copyright ?? 2000 Elsevier Science Ltd.

Spatiotemporal variations of the ⁹⁰Sr in the southern part of the Baltic Sea over the period of 2005-2010.

PubMed

Saniewski, Michał

2013-01-01

The Baltic Sea is one of the most contaminated seas by the radioactive isotope of strontium in the world; therefore the activity of ⁹⁰Sr is regularly controlled. Due to that fact, seawater samples for ⁹⁰Sr determination were collected at 16 stations located in the southern Baltic Sea between 2005 and 2010. In this period average activity of ⁹⁰Sr was 7.8 Bq m⁻³ and varied within the range from 3.0 Bq m⁻³ to 11.9 Bq m⁻³. Because the higher activity of ⁹⁰Sr was measured in the Baltic Sea than in the North Sea and rivers, inflows from the North Sea and the riverine runoff decreased ⁹⁰Sr activity in the Baltic Sea. The average ⁹⁰Sr activity in the bottom water along the offshore profile was 18% lower than that in the surface water and it was caused by an inflow of salt water from the North Sea. In the Vistula River mouth the average activity of ⁹⁰Sr in the surface water was about 15% lower than the average activity in the bottom waters. Coastal areas, relatively shallow with good mixing condition in the water column, were characterized by low variability in ⁹⁰Sr activity.

Status of rainbow smelt in the U.S. waters of Lake Ontario, 2013

USGS Publications Warehouse

Weidel, Brian C.; Connerton, Michael J.

2014-01-01

Rainbow Smelt Osmerus mordax are the second most abundant pelagic prey fish in Lake Ontario after Alewife Alosa psuedoharengus. The 2013, USGS/NYSDEC bottom trawl assessment indicated the abundance of Lake Ontario age-1 and older Rainbow Smelt decreased by 69% relative to 2012. Length frequency-based age analysis indicated that age-1 Rainbow Smelt constituted approximately 50% of the population, which is similar to recent trends where the proportion of age-1 has ranged from 95% to 42% of the population. While they constituted approximately half of the catch, the overall abundance index for age 1 was one of the lowest observed in the time series, potentially a result of cannibalism from the previous year class. Combined data from all bottom trawl assessments along the southern shore and eastern basin indicate the proportion of the fish community that is Rainbow Smelt has declined over the past 30 years. In 2013 the proportion of the pelagic fish catch (only pelagic species) that was Rainbow Smelt was the second lowest in the time series at 3.1%. Community diversity indices, based on bottom trawl catches, indicate that Lake Ontario fish community diversity, as assessed by bottom trawls, has sharply declined over the past 36 years and in 2013 the index was the lowest value in the time series. Much of this community diversity decline is driven by changes in the pelagic fish community and dominance of Alewife.

A note on the effect of wind waves on vertical mixing in Franks Tract, Sacramento-San Joaquin Delta, California, USA

USGS Publications Warehouse

Thompson, Janet K.; Jones, Nicole L.; Stephen G. Monismith,

2008-01-01

A one-dimensional numerical model that simulates the effects of whitecapping waves was used to investigate the importance of whitecapping waves to vertical mixing at a 3-meter-deep site in Franks Tract in the Sacramento-San Joaquin Delta over an 11-day period. Locally-generated waves of mean period approximately 2 s were generated under strong wind conditions; significant wave heights ranged from 0 to 0.3 m. A surface turbulent kinetic energy flux was used to model whitecapping waves during periods when wind speeds > 5 m s-1 (62% of observations). The surface was modeled as a wind stress log-layer for the remaining 38% of the observations. The model results demonstrated that under moderate wind conditions (5–8 m s-1 at 10 m above water level), and hence moderate wave heights, whitecapping waves provided the dominant source of turbulent kinetic energy to only the top 10% of the water column. Under stronger wind (> 8 m s-1), and hence larger wave conditions, whitecapping waves provided the dominant source of turbulent kinetic energy over a larger portion of the water column; however, this region extended to the bottom half of the water column for only 7% of the observation period. The model results indicated that phytoplankton concentrations close to the bed were unlikely to be affected by the whitecapping of waves, and that the formation of concentration boundary layers due to benthic grazing was unlikely to be disrupted by whitecapping waves. Furthermore, vertical mixing of suspended sediment was unlikely to be affected by whitecapping waves under the conditions experienced during the 11-day experiment. Instead, the bed stress provided by tidal currents was the dominant source of turbulent kinetic energy over the bottom half of the water column for the majority of the 11-day period.

Benthic foraminiferal response to the emergence of the Isthmus of Panama and coincident paleoceanographic changes

USGS Publications Warehouse

McDougall, K.

1996-01-01

Late Cenozoic benthic foraminiferal faunas from the Caribbean Deep Sea Drilling Project (DSDP) Site 502 (3052 m) and East Pacific DSDP Site 503 (3572 m) were analyzed to interpret bottom-water masses and paleoceanographic changes occurring as the Isthmus of Panama emerged. Major changes during the past 7 Myr occur at 6.7-6.2, 3.4, 2.0, and 1.1 Ma in the Caribbean and 6.7-6.4, 4.0-3.2, 2.1, 1.4, and 0.7 Ma in the Pacific. Prior to 6.7 Ma, benthic foraminiferal faunas at both sites indicate the presence of Antarctic Bottom Water (AABW). After 6.7 Ma benthic foraminiferal faunas indicate a shift to warmer water masses: North Atlantic Deep Water (NADW) in the Caribbean and Pacific Deep Water (PDW) in the Pacific. Flow of NADW may have continued across the rising sill between the Caribbean and Pacific until 5.6 Ma when the Pacific benthic foraminiferal faunas suggest a decrease in bottom-water temperatures. After 5.6 Ma deep-water to intermediate-water flow across the sill appears to have stopped as the bottom-water masses on either side of the sill diverge. The second change recorded by benthic foraminiferal faunas occurs at 3.4 Ma in the Caribbean and 4.0-3.2 Ma in the Pacific. At this time the Caribbean is flooded with cold AABW, which is either gradually warmed or is replaced by Glacial Bottom Water (GBW) at 2.0 Ma and by NADW at 1.1 Ma. These changes are related to global climatic events and to the depth of the sill between the Caribbean and Atlantic rather than the rising Isthmus of Panama. Benthic foraminiferal faunas at East Pacific Site 503 indicate a gradual change from cold PDW to warmer PDW between 4.0 and 3.2 Ma. The PDW is replaced by the warmer, poorly oxygenated PIW at 2.1 Ma. Although the PDW affects the faunas during colder intervals between 1.4 and 0.7 Ma, the PIW remains the principal bottom- water mass in the Guatemala Basin of the East Pacific.

Neodymium isotopes in authigenic phases, bottom waters and detrital sediments in the Gulf of Alaska and their implications for paleo-circulation reconstruction

NASA Astrophysics Data System (ADS)

Du, Jianghui; Haley, Brian A.; Mix, Alan C.

2016-11-01

The isotopic composition of neodymium (εNd) extracted from sedimentary Fe-Mn oxyhydroxide offers potential for reconstructing paleo-circulation, but its application depends on extraction methodology and the mechanisms that relate authigenic εNd to bottom water. Here we test methods to extract authigenic εNd from Gulf of Alaska (GOA) sediments and assess sources of leachate Nd, including potential contamination from trace dispersed volcanic ash. We show that one dominant phase is extracted via leaching of core-top sediments. Major and trace element geochemistry demonstrate that this phase is authigenic Fe-Mn oxyhydroxide. Contamination of leachate (authigenic) Nd from detrital sources is insignificant (<1%); our empirical results are consistent with established kinetic mineral dissolution rates and theory. Contamination of extracted εNd from leaching of volcanic ash is below analytical uncertainty. However, the εNd of core-top leachates in the GOA is consistently more radiogenic than bottom water. We infer that authigenic phases record pore water εNd, and the relationships of εNd among bottom waters, pore waters, authigenic phases and detrital sediments are primarily governed by the exposure time of bottom water to sea-floor sediments, rate of exchange across the sediment-water interface and the reactivity and composition of detrital sediments. We show that this conceptual model is applicable on the Pacific basin scale and provide a new framework to understand the role of authigenic phases in both modern and paleo-applications, including the use of authigenic εNd as a paleo-circulation tracer.

Comprehensive Characteristics of Bottom Sediments of Water Bodies of Various Types in the Kiliya Delta of the Danube River

EPA Science Inventory

The "triad" approach, including analysis of the total content of toxicants, bioassay of bottom sediments, and the study of the structure of zoo- and phytobenthos communities, was used in assessing the quality of bottom sediments. It has been found that the studied bottom sediment...

Estimating hydrodynamic roughness in a wave-dominated environment with a high-resolution acoustic Doppler profiler

USGS Publications Warehouse

Lacy, J.R.; Sherwood, C.R.; Wilson, D.J.; Chisholm, T.A.; Gelfenbaum, G.R.

2005-01-01

Hydrodynamic roughness is a critical parameter for characterizing bottom drag in boundary layers, and it varies both spatially and temporally due to variation in grain size, bedforms, and saltating sediment. In this paper we investigate temporal variability in hydrodynamic roughness using velocity profiles in the bottom boundary layer measured with a high-resolution acoustic Doppler profiler (PCADP). The data were collected on the ebb-tidal delta off Grays Harbor, Washington, in a mean water depth of 9 m. Significant wave height ranged from 0.5 to 3 m. Bottom roughness has rarely been determined from hydrodynamic measurements under conditions such as these, where energetic waves and medium-to-fine sand produce small bedforms. Friction velocity due to current u*c and apparent bottom roughness z0a were determined from the PCADP burst mean velocity profiles using the law of the wall. Bottom roughness kB was estimated by applying the Grant-Madsen model for wave-current interaction iteratively until the model u*c converged with values determined from the data. The resulting kB values ranged over 3 orders of magnitude (10-1 to 10-4 m) and varied inversely with wave orbital diameter. This range of kB influences predicted bottom shear stress considerably, suggesting that the use of time-varying bottom roughness could significantly improve the accuracy of sediment transport models. Bedform height was estimated from kB and is consistent with both ripple heights predicted by empirical models and bedforms in sonar images collected during the experiment. Copyright 2005 by the American Geophysical Union.

Sound Propagation in Shallow Water with an Inhomogeneous GAS-Saturated Bottom

NASA Astrophysics Data System (ADS)

Grigor'ev, V. A.; Petnikov, V. G.; Roslyakov, A. G.; Terekhina, Ya. E.

2018-05-01

We present the methods and results of numerical experiments studying the low-frequency sound propagation in one of the areas of the Arctic shelf with a randomly inhomogeneous gas-saturated bottom. The characteristics of the upper layer of bottom sedimentary rocks (sediments) used in calculations were obtained during a 3D seismic survey and trial drilling of the seafloor. We demonstrate the possibilities of substituting in numerical simulation a real bottom with a fluid homogeneous half-space where the effective value of the sound speed is equal to the average sound speed in the bottom, with averaging along the sound propagation path to a sediment depth of 0.6 wavelength in the bottom. An original technique is proposed for estimating the sound speed propagation in an upper inhomogeneous sediment layer. The technique is based on measurements of acoustic wave attenuation in water during waveguide propagation.

Depth distributions of uranium-236 and cesium-137 in the Japan/East Sea; toward the potential use as a new oceanic circulation tracer

NASA Astrophysics Data System (ADS)

Sakaguchi, A.; Kadokura, A.; Steier, P.; Takahashi, Y.; Shizuma, K.; Yamamoto, M.

2012-04-01

137Cs (T1/2=30.2 y) has been spread all over the world as a fission product of atmospheric nuclear weapons tests in the 1960s. This nuclide has been used as a powerful tool for oceanography due to the well-defined origin and conservative behaviour in water . However, the number of atoms has decayed already to one thirds compared with its initial levels, and it will become more difficult to measure. In this situation, we focus on 236U (T1/2=2.342-107 y) as a candidate for a new isotopic tracer for oceanography. The detection of 236U in the environment has become possible only recently, by the development of measuring techniques with high sensitivity based on AMS. Our group showed that global fallout from bomb tests contains 236U, which might be produced as nuclear reactions of 235U(n,γ) and/or 238U(n,3n). So 236U has been therefore globally distributed in the surface environment. Thus, 236U has a similar potential as a tracer for environmental dynamics as 137Cs, especially for oceanography. In this study, a comprehensive attempt was made to measure the concentration of 236U in marine samples such as water, suspended solid and bottom sediments to clarify the environmental behaviour of this isotope. Furthermore, the discussion of the circulation of deep and bottom water in "Miniature Ocean", the Japan Sea, has been attempted. Bottom sediments (4 sites) and seawater samples (7 sites) were collected from the Japan Sea. The sediment core was cut into 1 cm segments from the surface to 5 cm in depth within a few hours after the sampling. About 20 L of seawater samples were collected from some depths in each site, and immediately after the sampling, the water was filtered with 0.45 μm pore-size membrane-filters. After the appropriate pre-treatment for each sample, uranium isotope and 137Cs were measured with AMS and Ge-detector, respectively. 236U was successfully detected for all seawater samples, and 236U/238U atom ratios in seawater were in the range of (0.19-1.75)-10-9. The dissolved 236U concentration showed a subsurface maximum and decreased steeply with depth. The minimum value was found at a depth of 2500 m and bottom (about 3000 m in depth) in the northern and the southern areas, respectively. These profiles are markedly different from that of natural 238U which is nearly constant over the depth, suggesting that 236U has not yet reached steady state. For the SS sample, 236U could not be detected in significant levels. The total 236U inventory of the water column was estimated at 1012-1013 atom/m2. This value is nearly the same as the global fallout level (17.8-1012 atom/m2). 236U was also found in the bottom sediments, and the inventory was about 1/40 compared with that in water column. All above characters are comparable with 137Cs which is anthropogenic conservative nuclide in ocean. Actually, the diffusion coefficients for both nuclides show the nearly same value. The detail discussion including the circulation of deep-water in the Japan Sea will be given in our presentation.

Imaging Reservoir Siltation and Quaternary Stratigraphy Beneath the Mactaquac Headpond by Acoustic and Ground Penetrating Radar Sub-bottom Imaging

NASA Astrophysics Data System (ADS)

Grace, M.; Butler, K. E.; Peter, S.; Yamazaki, G.; Haralampides, K.

2016-12-01

The Mactaquac Hydroelectric Generating Station, located on the Saint John River in New Brunswick, Canada, is approaching the end of its life due to deterioration of the concrete structures. As part of an aquatic ecosystem study, designed to support a decision on the future of the dam, sediment in the headpond, extending 80 km upriver, is being examined. The focus of this sub-study lies in (i) mapping the thickness of sediments that have accumulated since inundation in 1968, and (ii) imaging the deeper glacial and post-glacial stratigraphy. Acoustic sub-bottom profiling surveys were completed during 2014 and 2015. An initial 3.5 kHz chirp sonar survey proved ineffective, lacking in both resolution and depth of the penetration. A follow-up survey employing a boomer-based "Seistec" sediment profiler provided better results, resolving sediment layers as thin as 12 cm, and yielding coherent reflections from the deeper Quaternary sediments. Post-inundation sediments in the lowermost 25 km of the headpond, between the dam and Bear Island, are interpreted to average 26 cm in thickness with the thickest deposits (up to 65 cm) in deep water areas overlying the pre-inundation riverbed west of Snowshoe Island, and south and east of Bear Island. A recent coring program confirmed the presence of silty sediment and showed good correlation with the Seistec thickness estimates. In the 15 km stretch upriver of Bear Island to Nackawic, the presence of gas in the uppermost sediments severely limits sub-bottom penetration and our ability to interpret sediment thicknesses. Profiles acquired in the uppermost 40 km reach of the headpond, extending to Woodstock, show a strong, positive water bottom reflection and little to no sub-bottom penetration, indicating the absence of soft post-inundation sediment. Deeper reflections observed within 5 km of the dam reveal a buried channel cut into glacial till, extending up to 20 m below the water bottom. Channel fill includes a finely laminated unit interpreted to be glaciolacustrine clay-silt and a possible esker - similar to stratigraphy found 20 - 30 km downriver at Fredericton. Future plans include a small scale survey in late summer, 2016 to evaluate the suitability of waterborne ground penetrating radar (GPR) profiling as an alternative to acoustic profiling in areas of gas-charged sediment.

Valorization of MSWI bottom ash for biogas desulfurization: Influence of biogas water content.

PubMed

Fontseré Obis, Marta; Germain, Patrick; Troesch, Olivier; Spillemaecker, Michel; Benbelkacem, Hassen

2017-02-01

In this study an alternative valorization of Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) for H 2 S elimination from landfill biogas was evaluated. Emphasis was given to the influence of water content in biogas on H 2 S removal efficiency by BA. A small-scale pilot was developed and implemented in a landfill site located in France. A new biogas analyzer was used and allowed real-time continuous measurement of CH 4 , CO 2 , O 2 , H 2 S and H 2 O in raw and treated biogas. The H 2 S removal efficiency of bottom ash was evaluated for different inlet biogas humidities: from 4 to 24g water /m 3 . The biogas water content was found to greatly affect bottom ash efficiency regarding H 2 S removal. With humid inlet biogas the H 2 S removal was almost 3 times higher than with a dry inlet biogas. Best removal capacity obtained was 56gH 2 S/kgdryBA. A humid inlet biogas allows to conserve the bottom ash moisture content for a maximum H 2 S retention. Copyright © 2016 Elsevier Ltd. All rights reserved.

Geoacoustic inversion with two source-receiver arrays in shallow water.

PubMed

Sukhovich, Alexey; Roux, Philippe; Wathelet, Marc

2010-08-01

A geoacoustic inversion scheme based on a double beamforming algorithm in shallow water is proposed and tested. Double beamforming allows identification of multi-reverberated eigenrays propagating between two vertical transducer arrays according to their emission and reception angles and arrival times. Analysis of eigenray intensities yields the bottom reflection coefficient as a function of angle of incidence. By fitting the experimental reflection coefficient with a theoretical prediction, values of the acoustic parameters of the waveguide bottom can be extracted. The procedure was initially tested in a small-scale tank experiment for a waveguide with a Plexiglas bottom. Inversion results for the speed of shear waves in Plexiglas are in good agreement with the table values. A similar analysis was applied to data collected during an at-sea experiment in shallow coastal waters of the Mediterranean. Bottom reflection coefficient was fitted with the theory in which bottom sediments are modeled as a multi-layered system. Retrieved bottom parameters are in quantitative agreement with those determined from a prior inversion scheme performed in the same area. The present study confirms the interest in processing source-receiver array data through the double beamforming algorithm, and indicates the potential for application of eigenray intensity analysis to geoacoustic inversion problems.

A method for evaluating the evolution of clogging: application to the Pampulha Campus infiltration system (Brazil).

PubMed

Barraud, S; Gonzalez-Merchan, C; Nascimento, N; Moura, P; Silva, A

2014-01-01

In order to evaluate the hydraulic performance of stormwater infiltration trenches, a study was undertaken to assess clogging and its distribution between the bottom and the sides. The method used was based on the calibration of the hydraulic resistance event by event according to Bouwer's model and applied to a demonstration trench in Belo-Horizonte monitored in the framework of the European Project Switch. The calibration was performed by minimizing the distance between measured and modeled infiltration flow rates and by using continuous measurements of rainfall, inflow, water temperature and depth in the trench. The study showed that the methodology and particularly Bouwer's model was able to produce satisfactory results. It revealed a significant clogging evolution within a year, with global resistance increasing by a factor of 9. A significant difference between the bottom and the sides was observed; the bottom being more rapidly prone to clogging. Sudden fluctuations of the hydraulic resistance of the bottom were found that could be explained by very high concentrations of total suspended solids from inflows (about 2,000 mg/L). Clogging of the sides evolves over the time but with a very low rate.

The Hillary Canyon and the Iselin Bank (Eastern Ross Sea, Antarctica): Alongslope and Downslope Route For Ross Sea Bottom Water

NASA Astrophysics Data System (ADS)

De Santis, L.; Bergamasco, A.; Colizza, E.; Geletti, R.; Accaino, F.; Wardell, N.; Olivo, E.; Petronio, L.; Henrys, S. A.; Black, J.; Mckay, R. M.; Bohm, G.

2015-12-01

The modern seabed of the Antarctic continental slope generally does not show a rugged geomorphology. Channel systems incise the lower continental rise, but in most cases they are inherited features formed as channel-levee turbiditic systems during past, more temperate times. The Hillary Canyon cuts the eastern Ross Sea continental slope and rise, to the Southeast of the Iselin Bank, and is directly connected to the Glomar Challenger Trough on the continental shelf. Cold dense salty water forms today in the Ross Sea polynya, spreads below the Ross Ice Shelf, becomes supercooled, fills up the landward deepening Glomar Challenger Trough and then spills over the sill of the shelf edge and flows downslope, often along the Hillary Canyon, in a geostrophic way, deviated westwards by the Coriolis Force, but sometimes also with a cascading a-geostrophic behaviour. This supercold water signal was found on the continental slope down to 1200 m depth. The shape of this tongue of modified ISW, whose thickness reaches up to 100 m, is very narrow, suggesting that the overflow occurs in very localized areas along the slope. Here we combine seismic stratigraphy analysis of multichannel seismic reflection profiles, box and gravity cores in the Hillary Canyon and along the eastern flank of the Iselin Bank, with seabed bathymetry and numerical modelling of thevertical and spatial distribution of the water masses, in order to identify modern and past pathways of the Ross Sea Bottom Water current. The results of this work show that the Hillary Canyon and the sediment mounds that formed along its flanks have been active since early Miocene times. Sediment drift-moat features and sediment waves are indicative of strong Northwest bottom currents reworking the seabed sediments at different water depths along the slope, possibly since the late Miocene. These sediment drifts are some of the targets of the IODP proposal 751-full.

Transient Point Infiltration In The Unsaturated Zone

NASA Astrophysics Data System (ADS)

Buecker-Gittel, M.; Mohrlok, U.

The risk assessment of leaking sewer pipes gets more and more important due to urban groundwater management and environmental as well as health safety. This requires the quantification and balancing of transport and transformation processes based on the water flow in the unsaturated zone. The water flow from a single sewer leakage could be described as a point infiltration with time varying hydraulic conditions externally and internally. External variations are caused by the discharge in the sewer pipe as well as the state of the leakage itself. Internal variations are the results of microbiological clogging effects associated with the transformation processes. Technical as well as small scale laboratory experiments were conducted in order to investigate the water transport from an transient point infiltration. From the technical scale experiment there was evidence that the water flow takes place under transient conditions when sewage infiltrates into an unsaturated soil. Whereas the small scale experiments investigated the hydraulics of the water transport and the associated so- lute and particle transport in unsaturated soils in detail. The small scale experiment was a two-dimensional representation of such a point infiltration source where the distributed water transport could be measured by several tensiometers in the soil as well as by a selective measurement of the discharge at the bottom of the experimental setup. Several series of experiments were conducted varying the boundary and initial con- ditions in order to derive the important parameters controlling the infiltration of pure water from the point source. The results showed that there is a significant difference between the infiltration rate in the point source and the discharge rate at the bottom, that could be explained by storage processes due to an outflow resistance at the bottom. This effect is overlayn by a decreasing water content decreases over time correlated with a decreasing infiltration rate. As expected the initial conditions mainly affects the time scale for the water transport. Additionally, the influence of preferential flow paths on the discharge distribution could be found due to the heterogenieties caused by the filling and compaction process of the sandy soil.

Inorganic and organic nitrogen uptake by phytoplankton and heterotrophic bacteria in the stratified Mid-Atlantic Bight

NASA Astrophysics Data System (ADS)

Bradley, Paul B.; Sanderson, Marta P.; Frischer, Marc E.; Brofft, Jennifer; Booth, Melissa G.; Kerkhof, Lee J.; Bronk, Deborah A.

2010-08-01

Little is known about the relative importance of inorganic and organic nitrogen (N) sources in fueling production of phytoplankton versus heterotrophic bacteria on the continental shelf. This issue was addressed during two diel experiments conducted in the Mid-Atlantic Bight at the Long-term Ecosystem Observatory, LEO-15, off southern New Jersey. Uptake of 15N-labeled ammonium (NH 4+), nitrate (NO 3-), and nitrite (NO 2-), and dual-labeled ( 15N and 13C) urea and dissolved free amino acids was measured in water taken from the surface and bottom mixed layers approximately every 4 h over two 24 h periods in July 2002. Two methods were used to quantify 15N uptake rates: (1) traditional filtration into various phytoplankton and bacterial size classes, and (2) flow cytometric (FCM) sorting of autotrophic cells based on the presence of chlorophyll autofluorescence. Due to a strong pycnocline, the nutrient composition was quite distinct between the surface and bottom mixed layers. Dissolved organic N (DON) comprised >99% of the total dissolved N (TDN) pool in surface waters, whereas the bottom-water TDN pool was roughly divided between NH 4+, NO 3-, and DON. Urea was the dominant N form used by all fractions at the surface, and although phytoplankton >3 μm was responsible for most of the urea uptake, bacterial use was detected using stable isotopes and also suggested by ureC sequence analysis. The majority of ureC sequences recovered from the 0.2-0.8 μm fraction belonged to members of the Alphaproteobacteria (46%), whereas those of the 0.8-3.0 μm size class consisted primarily of Cyanobacteria (70%). In contrast to the surface, N uptake in the bottom layer was dominated by NH 4+. The bacterial fraction was responsible for 20-49% of the size-fractionated NH 4+ and NO 3- uptake in surface samples and 36-93% at the bottom. These results suggest that organic N, such as urea, is a viable source of N nutrition to phytoplankton forced to compete with heterotrophic bacteria for limited inorganic N.

Dissolved and Colloidal Trace Elements in the Mississippi River Delta Outflow after Hurricanes Katrina and Rita

NASA Astrophysics Data System (ADS)

Shim, M.; Swarzenski, P. W.; Shiller, A. M.

2010-12-01

The Mississippi River (MR) plays an important role as a major fluvial source of dissolved and particulate materials for the Gulf of Mexico (GOM). This region is periodically disturbed by tropical weather systems including major hurricanes. Such storms have the potential to stir up the normally stratified water column of the Louisiana Shelf and thus can serve as a mechanism for the abrupt termination of seasonal bottom water hypoxia. Additionally, strong tropical systems can cause the resuspension of shelf bottom sediments which could result in the injection of trace elements into the water column. In the summer of 2005, two major hurricanes, Katrina and Rita, passed over the Louisiana Shelf within a month of each other. Three weeks after Rita, we participated in a survey of the waters of the Mississippi River delta outflow, examining the distributions of trace elements (including Ba, Co, Cr, Cs, Cu, Fe, Mn, Ni, Re, U, V, and Zn) in a comparison with previous results in this area. We indeed observed that there was limited stratification on the shelf and that bottom waters were no longer hypoxic. This resulted, for instance, in bottom water dissolved Mn being lower than is typically observed during hypoxia, but with concentrations still compatible with Mn-O2 trends previously reported. Interestingly, for no element were we able to identify an obvious effect of sediment resuspension on its distribution. In general, elemental distributions were compatible with previous observations in the Mississippi outflow system. Co and Re, which have not been reported for this system previously, showed behavior consistent with other systems: input for Co likely from desorption and conservative mixing for Re. For Cs, an element for which there is little information regarding its estuarine behavior, conservative mixing was also observed. Our filtration method, which allowed us to distinguish the dissolved (<0.02 µm) from colloidal (0.02 - 0.45 µm) phase, revealed significant colloidal fractions for Fe and Zn, only. For Fe, the colloidal phase was the dominant fraction and was rapidly removed at low salinity. Dissolved Fe, in contrast, persisted out to mid-salinities, being removed in a similar fashion to nitrate. This ability to distinguish the smaller Fe (likely dominantly organically complexed) from larger colloidal suspensates may be useful in better interpreting the bioavailablity of the Fe in estuarine systems.

Bottom water production variability in the Ross Sea slope during the Late-Pleistocene-Holocene as revealed by benthic foraminifera and sediment geochemistry

NASA Astrophysics Data System (ADS)

Asioli, A.; Langone, L.; Tateo, F.; Giannossi, M. L.; Giglio, F.; Summa, V.; Piva, A.; Ridente, D.; Trincardi, F.

2009-04-01

The Antarctic area produces bottom waters that ventilate the vast majority of the deep basins in the rest of the world ocean. The rate of formation in the source area and the strength of these cold bottom waters affect their flow toward the equator and are key factors affecting the Global Thermohaline Circulation during modern and past climate conditions. We present the results of a multidisciplinary study carried out on a core collected in 2377m of water depth on the slope off the Drygalski Basin (Ross Sea), along the modern path of the bottom waters. The goal of this research is to detect a qualitative signal of possible changes in the rate of bottom water production during the Late Pleistocene-Holocene by integrating micropaleontological and geochemical proxies. The micropaleontological signal is represented by the quantitative and qualitative variations of the agglutinated benthic foraminifera assemblages, while the amount of TOC, nitrogen, δ13C, δ15N, biogenic silica, CaCO3 in the sediment, along with the bulk rock mineralogy, provide information on the paleoproductivity and allow reconstruction of changes in the paleocirculation. The chronology is supported by 14C AMS datings on organic matter. Although this study is still in progress, the results obtained allow the following observations: 1) the Holocene sequence includes a major turnover around 8-8.5 calib kyr BP, leading to reduced nutrient utilization, probably reflecting an increased nutrient supply induced by an enhanced Upper Circumpolar Deep Water upwelling; 2) within this general context, the total concentration of benthic foraminifera preserved in the fossil component records millennial scale cycles of variable amplitude after 8.5 calib kyr BP and to present time. This oscillatory trend is paralleled by other parameters, such as the magnetic susceptibility, the dry density, the sheet silicates and the δ15N; 3) minima in foraminifera concentration reflect relatively increased dissolution, weaker bottom currents (minima in dry density=higher amount of fine fraction), and lower nutrient supply; maxima in foraminifera concentration indicate better preservation, higher benthic productivity and/or better oxygenation at bottom, stronger bottom currents (maxima in dry density) and relatively higher nutrient supply; 4) these cycles are interpreted to reflect a relatively higher (maxima in forams concentration) or lower (minima in forams concentration) rate of bottom water formation; 5) between 8.5 and 6 kyr BP the amplitude of these cycles (and particularly those with increased rates of bottom water formation) is higher than the subsequent ones. We equate this interval with the early part of the Middle Holocene Climatic Optimum of the literature; 6) the condensed/hiatus interval centred at ca. 3.5-4 kyr BP does not seem to mark a major change in the general pattern. Nevertheless, this feature is time-equivalent to a major change in the circulation pattern in other Antarctic regions, such as the Antarctic Peninsula. This major change consists in oscillations between two contrasting circulation modes dominated respectively by: a) Upper Circumpolar Deep Water and b) shelf-water formation. This major change can therefore be ascribed to the southward migration of the Intertropical Convergence Zone vs. ENSO prevalence, respectively.

Water quality observations of ice-covered, stagnant, eutrophic water bodies and analysis of influence of ice-covered period on water quality

NASA Astrophysics Data System (ADS)

sugihara, K.; Nakatsugawa, M.

2013-12-01

The water quality characteristics of ice-covered, stagnant, eutrophic water bodies have not been clarified because of insufficient observations. It has been pointed out that climate change has been shortening the duration of ice-cover; however, the influence of climate change on water quality has not been clarified. This study clarifies the water quality characteristics of stagnant, eutrophic water bodies that freeze in winter, based on our surveys and simulations, and examines how climate change may influence those characteristics. We made fixed-point observation using self-registering equipment and vertical water sampling. Self-registering equipment measured water temperature and dissolved oxygen(DO).vertical water sampling analyzed biological oxygen demand(BOD), total nitrogen(T-N), nitrate nitrogen(NO3-N), nitrite nitrogen(NO2-N), ammonium nitrogen(NH4-N), total phosphorus(TP), orthophosphoric phosphorus(PO4-P) and chlorophyll-a(Chl-a). The survey found that climate-change-related increases in water temperature were suppressed by ice covering the water area, which also blocked oxygen supply. It was also clarified that the bottom sediment consumed oxygen and turned the water layers anaerobic beginning from the bottom layer, and that nutrient salts eluted from the bottom sediment. The eluted nutrient salts were stored in the water body until the ice melted. The ice-covered period of water bodies has been shortening, a finding based on the analysis of weather and water quality data from 1998 to 2008. Climate change was surveyed as having caused decreases in nutrient salts concentration because of the shortened ice-covered period. However, BOD in spring showed a tendency to increase because of the proliferation of phytoplankton that was promoted by the climate-change-related increase in water temperature. To forecast the water quality by using these findings, particularly the influence of climate change, we constructed a water quality simulation model that incorporates the freezing-over of water bodies. The constructed model shows good temporal and spatial reproducibility and enables water quality to be forecast throughout the year, including during the ice-covered period. The forecasts using the model agree well with the survey results of shortened ice period and climate-change-related increase in the BOD in spring. From the result of calculations and observations, it is suggested that water quality of spring has been deteriorate because of freezing period to be shortened due to temperature rising.

Erosional and depositional patterns associated with the 1993 Missouri River floods inferred from SIR-C and TOPSAR radar data

USGS Publications Warehouse

Izenberg, N.R.; Arvidson, R. E.; Brackett, R.A.; Saatchi, S.S.; Osburn, G.R.; Dohrenwend, J.

1996-01-01

The Missouri River floods of 1993 caused significant and widespread damage to the floodplains between Kansas City and St. Louis. Immediately downstream of levee breaks, flood waters scoured the bottoms. As the floodwaters continued, they spread laterally and deposited massive amounts of sand as crevasse splays on top of agricultural fields. We explore the use of radar interferometry and backscatter data for quantitative estimation of scour and deposition for Jameson Island/Arrow Rock Bottoms and Lisbon Bottoms, two bottoms that were heavily damaged during the floods and subsequently abandoned. Shuttle imaging radar C (SIR-C) L band (24 cm) HH (horizontally transmitted and horizontally received) radar backscatter data acquired in October 1994 were used together with a distorted Born approximation canopy scattering model to determine that the abundance of natural leafy forbs controlled the magnitude of backscatter for former agricultural fields. Forb areal density was found to be inversely correlated with thickness of sand deposited during the floods, presumably because thick sands prevented roots from reaching nutrient rich, moist bottoms soils. Using the inverse relationship, a lower bound for the mass of sand added was found to be 6.3 million metric tons over the 17 km2 study area. Digital elevation data from topographic synthetic aperture radar (TOPSAR) C band (5.6 cm) interferometric observations acquired in August 1994 were compared to a series of elevation profiles collected on the ground. Vertical errors in TOPSAR were estimated to range from 1 to 2 m, providing enough accuracy to generate an estimate of total mass (4.7 million metric tons) removed during erosion of levees and scour of the bottoms terrains. Net accretion of material to the study areas is consistent with the geologic record of major floods where sediment-laden floodwaters crested over natural levees, initially scoured into the bottoms, and then deposited sands as crevasse splays as the flows spread out and slowed by frictional dissipation. The addition of artificial levees to the Missouri River system has undoubtedly enhanced flood damage, although quantitative estimation of the degree of enhancement will require additional work. Copyright 1996 by the American Geophysical Union.

Erosional and depositional patterns associated with the 1993 Missouri River floods inferred from SIR-C and TOPSAR radar data

NASA Astrophysics Data System (ADS)

Izenberg, N. R.; Arvidson, R. E.; Brackett, R. A.; Saatchi, S. S.; Osburn, G. R.; Dohrenwend, J.

1996-10-01

The Missouri River floods of 1993 caused significant and widespread damage to the floodplains between Kansas City and St. Louis. Immediately downstream of levee breaks, flood waters scoured the bottoms. As the floodwaters continued, they spread laterally and deposited massive amounts of sand as crevasse splays on top of agricultural fields. We explore the use of radar interferometry and backscatter data for quantitative estimation of scour and deposition for Jameson Island/Arrow Rock Bottoms and Lisbon Bottoms, two bottoms that were heavily damaged during the floods and subsequently abandoned. Shuttle imaging radar C (SIR-C) L band (24 cm) HH (horizontally transmitted and horizontally received) radar backscatter data acquired in October 1994 were used together with a distorted Born approximation canopy scattering model to determine that the abundance of natural leafy forbs controlled the magnitude of backscatter for former agricultural fields. Forb areal density was found to be inversely correlated with thickness of sand deposited during the floods, presumably because thick sands prevented roots from reaching nutrient rich, moist bottoms soils. Using the inverse relationship, a lower bound for the mass of sand added was found to be 6.3 million metric tons over the 17 km2 study area. Digital elevation data from topographic synthetic aperture radar (TOPSAR) C band (5.6 cm) interferometric observations acquired in August 1994 were compared to a series of elevation profiles collected on the ground. Vertical errors in TOPSAR were estimated to range from 1 to 2 m, providing enough accuracy to generate an estimate of total mass (4.7 million metric tons) removed during erosion of levees and scour of the bottoms terrains. Net accretion of material to the study areas is consistent with the geologic record of major floods where sediment-laden floodwaters crested over natural levees, initially scoured into the bottoms, and then deposited sands as crevasse splays as the flows spread out and slowed by frictional dissipation. The addition of artificial levees to the Missouri River system has undoubtedly enhanced flood damage, although quantitative estimation of the degree of enhancement will require additional work.

Comparative analysis of different loading conditions on large container ships from the perspective of the stability requirement

NASA Astrophysics Data System (ADS)

Stanca, C.; Acomi, N.; Ancuta, C.; Georgescu, S.

2015-11-01

Container ships carry cargoes that are considered light from the weight point of view, compared to their volumetric capacity. This fact makes the still water vertical bending moment to be in hogging condition. Thus, the double bottom structure is permanent subject to compressive load. With the enlargement of container ships to the Post Panamax vessels, the breadth to depth ratio tends to be increased comparative to those of Panamax container ships that present restriction related to maximum breadth of the ship.The current studies on new build models reveal the impossibility for Panamax container ships to comply with the minimum metacentric height value of stability without loading ballast water in the double bottom tanks. In contrast, the Post-Panamax container ships, as resulted from metacentric height calculation, have adequate stability even if the ballast water is not loaded in the double bottom tanks. This analysis was conducted considering two partially loaded port-container vessels. Given the minimization of ballast quantities, the frequency with which the still water vertical bending moment reaches close to the allowable value increases.This study aims to analyse the ships’ behaviour in partially loaded conditions and carrying ballast water in the double bottom tanks. By calculating the metacentric height that influences the stability of the partially loaded port container vessels, this study will emphasize the critical level of loading condition which triggers the uptake of ballast water in the double bottom tanks, due to metacentric height variation.

Increased thermohaline stratification as a possible cause for an ocean anoxic event in the Cretaceous period.

PubMed

Erbacher, J; Huber, B T; Norris, R D; Markey, M

2001-01-18

Ocean anoxic events were periods of high carbon burial that led to drawdown of atmospheric carbon dioxide, lowering of bottom-water oxygen concentrations and, in many cases, significant biological extinction. Most ocean anoxic events are thought to be caused by high productivity and export of carbon from surface waters which is then preserved in organic-rich sediments, known as black shales. But the factors that triggered some of these events remain uncertain. Here we present stable isotope data from a mid-Cretaceous ocean anoxic event that occurred 112 Myr ago, and that point to increased thermohaline stratification as the probable cause. Ocean anoxic event 1b is associated with an increase in surface-water temperatures and runoff that led to decreased bottom-water formation and elevated carbon burial in the restricted basins of the western Tethys and North Atlantic. This event is in many ways similar to that which led to the more recent Plio-Pleistocene Mediterranean sapropels, but the greater geographical extent and longer duration (approximately 46 kyr) of ocean anoxic event 1b suggest that processes leading to such ocean anoxic events in the North Atlantic and western Tethys were able to act over a much larger region, and sequester far more carbon, than any of the Quaternary sapropels.

Fate of internal waves on a shallow shelf

NASA Astrophysics Data System (ADS)

Davis, Kristen; Arthur, Robert; Reid, Emma; Decarlo, Thomas; Cohen, Anne

2017-11-01

Internal waves strongly influence the physical and chemical environment of coastal ecosystems worldwide. We report novel observations from a distributed temperature sensing (DTS) system that tracked the transformation of internal waves from the shelf break to the surf zone over a shelf-slope region of a coral atoll in the South China Sea. The spatially-continuous view of the near-bottom temperature field provided by the DTS offers a perspective of physical processes previously available only in laboratory settings or numerical models. These processes include internal wave reflection off a natural slope, shoreward transport of dense fluid within trapped cores, internal ``tide pools'' (dense water left behind after the retreat of an internal wave), and internal run-down (near-bottom, offshore-directed jets of water preceding a breaking internal wave). Analysis shows that the fate of internal waves on this shelf - whether they are transmitted into shallow waters or reflected back offshore - is mediated by local water column density and shear structure, with important implications for nearshore distributions of energy, heat, and nutrients. We acknowledge the US Army Research Laboratory DoD Supercomputing Resource Center for computer time on Excalibur, which was used for the numerical simulations in this work. Funding for field work supported by Academia Sinica and for K.D. and E.R. from NSF.

Occurrence and distribution of perfluoroalkyl substances (PFASs) in surface water and bottom water of the Shuangtaizi Estuary, China.

PubMed

Shao, Mihua; Ding, Guanghui; Zhang, Jing; Wei, Lie; Xue, Huanhuan; Zhang, Nannan; Li, Yang; Chen, Guanqun; Sun, Yeqing

2016-09-01

Perfluoroalkyl substances (PFASs) have been recognized as emerging environmental pollutants. However, there is limited information on the contamination level and spatial distribution of PFASs in the Shuangtaizi Estuary, where the Shuangtaizi Hekou Nature Reserve is located. In the present study, the contamination level and spatial distribution of PFASs in surface water (approximately 0.5 m below the surface) and bottom water (about 0.5 m above the bottom) of the Shuangtaizi Estuary were investigated. The data indicated that the Shuangtaizi Estuary was commonly contaminated by PFASs. The total concentration of PFASs in surface and bottom water of the Shuangtaizi Estuary ranged from 66.2 to 185 ng L(-1) and from 44.8 to 209 ng L(-1), respectively. The predominant PFASs were perfluorobutanoic acid (PFBA), perfluoropentanoic acid, perfluorooctanoic acid, perfluorohexanoic acid and perfluorobutane sulfonate (PFBS). In general, PFAS concentrations in surface water samples were lower than those in bottom water samples. The spatial distribution of PFASs in the Shuangtaizi Estuary was mainly affected by particular landform, tide and residual currents in Liaodong Bay. The total mass flux of 15 PFASs from the Shuangtaizi River to Liaodong Bay was estimated to be 352 kg year(-1), which was lower than the total flux from the Daling River and the Daliao River. As short-chain PFASs, such as PFBS and PFBA, have been the prevalent compounds in some places and are continuously produced and used, long-term monitoring and effective pollution controls are suggested. Copyright © 2016 Elsevier Ltd. All rights reserved.

Estimating Bottom Water Dissolved Oxygen in the Mississippi River Gulf Outlet and Gulf Intracoastal Waterway Resulting from Proposed Structures

DTIC Science & Technology

2008-09-01

used in the analysis. The analytical approach assumes steady-state, summer conditions applied to a continuously stirred tank reactor ( CSTR ). CSTR ...constituent due to the fully mixed CSTR assumption. Thus, there is no spatial dimensionality. The DO CSTR model is solved using a spreadsheet...For this study, the CSTR represents the bottom meter of water along the reach of the channel being assessed. A unit bottom layer thickness of 1 m

Parameterized code SHARM-3D for radiative transfer over inhomogeneous surfaces.

PubMed

Lyapustin, Alexei; Wang, Yujie

2005-12-10

The code SHARM-3D, developed for fast and accurate simulations of the monochromatic radiance at the top of the atmosphere over spatially variable surfaces with Lambertian or anisotropic reflectance, is described. The atmosphere is assumed to be laterally uniform across the image and to consist of two layers with aerosols contained in the bottom layer. The SHARM-3D code performs simultaneous calculations for all specified incidence-view geometries and multiple wavelengths in one run. The numerical efficiency of the current version of code is close to its potential limit and is achieved by means of two innovations. The first is the development of a comprehensive precomputed lookup table of the three-dimensional atmospheric optical transfer function for various atmospheric conditions. The second is the use of a linear kernel model of the land surface bidirectional reflectance factor (BRF) in our algorithm that has led to a fully parameterized solution in terms of the surface BRF parameters. The code is also able to model inland lakes and rivers. The water pixels are described with the Nakajima-Tanaka BRF model of wind-roughened water surface with a Lambertian offset, which is designed to model approximately the reflectance of suspended matter and of a shallow lake or river bottom.

Parameterized code SHARM-3D for radiative transfer over inhomogeneous surfaces

NASA Astrophysics Data System (ADS)

Lyapustin, Alexei; Wang, Yujie

2005-12-01

The code SHARM-3D, developed for fast and accurate simulations of the monochromatic radiance at the top of the atmosphere over spatially variable surfaces with Lambertian or anisotropic reflectance, is described. The atmosphere is assumed to be laterally uniform across the image and to consist of two layers with aerosols contained in the bottom layer. The SHARM-3D code performs simultaneous calculations for all specified incidence-view geometries and multiple wavelengths in one run. The numerical efficiency of the current version of code is close to its potential limit and is achieved by means of two innovations. The first is the development of a comprehensive precomputed lookup table of the three-dimensional atmospheric optical transfer function for various atmospheric conditions. The second is the use of a linear kernel model of the land surface bidirectional reflectance factor (BRF) in our algorithm that has led to a fully parameterized solution in terms of the surface BRF parameters. The code is also able to model inland lakes and rivers. The water pixels are described with the Nakajima-Tanaka BRF model of wind-roughened water surface with a Lambertian offset, which is designed to model approximately the reflectance of suspended matter and of a shallow lake or river bottom.

Mg/Ca ratios of the benthic foraminifera Oridorsalis umbonatus obtained by laser ablation from core top sediments: Relationship to bottom water temperature

NASA Astrophysics Data System (ADS)

Rathmann, SöHnke; Hess, Silvia; Kuhnert, Henning; Mulitza, Stefan

2004-12-01

A laser ablation system connected to an inductively coupled plasma mass spectrometer was used to determine Mg/Ca ratios of the benthic foraminifera Oridorsalis umbonatus. A set of modern core top samples collected along a depth transect on the continental slope off Namibia (320-2300 m water depth; 2.9° to 10.4°C) was used to calibrate the Mg/Ca ratio against bottom water temperature. The resulting Mg/Ca-bottom water temperature relationship of O. umbonatus is described by the exponential equation Mg/Ca = 1.528*e0.09*BWT. The temperature sensitivity of this equation is similar to previously published calibrations based on Cibicidoides species, suggesting that the Mg/Ca ratio of O. umbonatus is a valuable proxy for thermocline and deep water temperature.

Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in and near Stillwater Wildlife Management Area, Churchill County, Nevada, 1986-87

USGS Publications Warehouse

Hoffman, R.J.; Hallock, R.J.; Rowe, T.G.; Lico, M.S.; Burge, H.L.; Thompson, S.P.

1990-01-01

A reconnaissance was initiated in 1986 to determine whether the quality of irrigation-drainage water in and near the Stillwater Wildlife Management Area, Nevada, has caused or has potential to cause harmful effects on human health, fish, wildlife, or other beneficial uses of water. Samples of surface and groundwater, bottom sediment, and biota were collected from sites upstream and downstream from the Fallon agricultural area in the Carson Desert, and analyzed for potentially toxic trace elements. Other analysis included radioactive substances, major dissolved constituents, and nutrients in water, and pesticide residues in bottom sediment and biota. In areas affected by irrigation drainage, the following constituents were found to commonly exceed baseline concentrations or recommended criteria for protection of aquatic life or propagation of wildlife: In water, arsenic, boron, dissolved solids, molybdenum, sodium, and un-ionized ammonia; in bottom sediments, arsenic, lithium, mercury, molybdenum, and selenium; and in biota, arsenic, boron, chromium, copper, mercury, selenium, and zinc. In some wetlands, selenium and mercury appeared to be biomagnified, and arsenic bioaccumulated. Pesticides contamination in bottom sediments and biota was insignificant. Adverse biological effects observed during this reconnaissance included gradual vegetative changes and species loss, fish die-offs, waterfowl disease epidemics, and persistent and unexplained deaths of migratory birds. (USGS)

Trace-element budgets in the Ohio/Sunbury shales of Kentucky: Constraints on ocean circulation and primary productivity in the Devonian-Mississippian Appalachian Basin

USGS Publications Warehouse

Perkins, R.B.; Piper, D.Z.; Mason, C.E.

2008-01-01

The hydrography of the Appalachian Basin in late Devonian-early Mississippian time is modeled based on the geochemistry of black shales and constrained by others' paleogeographic reconstructions. The model supports a robust exchange of basin bottom water with the open ocean, with residence times of less than forty years during deposition of the Cleveland Shale Member of the Ohio Shale. This is counter to previous interpretations of these carbon-rich units having accumulated under a stratified and stagnant water column, i.e., with a strongly restricted bottom bottom-water circulation. A robust circulation of bottom waters is further consistent with the palaeoclimatology, whereby eastern trade-winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment, fresh waters, and riverine nutrients. The model suggests that primary productivity was high (~ 2??g C m- 2 d- 1), although no higher than in select locations in the ocean today. The flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments. Calculations based on the average accumulation rate of the marine fraction of Ni suggest the flux of organic carbon settling out of the water column was approximately 9% of primary productivity, versus an accumulation rate (burial) of organic carbon of 0.5% of primary productivity. Trace-element ratios of V:Mo and Cr:Mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic (sulfate reducing) during deposition of the Huron Shale Member of the Ohio Shale to predominantly suboxic (nitrate reducing) during deposition of the Cleveland Shale Member and the Sunbury Shale, but with anoxic conditions occurring intermittently throughout this period. ?? 2008 Elsevier B.V.

What does atmospheric nitrogen contribute to the Gulf of Mexico area of oxygen depletion?

NASA Astrophysics Data System (ADS)

Rabalais, N. N.

2017-12-01

The northern Gulf of Mexico influenced by the freshwater discharge and nutrient loads of the Mississippi River watershed is the location of the world's second largest human-caused area of coastal hypoxia. Over 500 more anthropogenic `dead zones' exist in coastal waters. The point source inputs within the Mississippi River watershed account for about ten per cent of the total nitrogen inputs to the Mississippi River, with the remaining being nonpoint source. Atmospheric nitrogen makes up about sixteen per cent of the nonpoint source input of nitrogen. Most of the NOx is generated within the Ohio River watershed from the burning of fossil fuels. Some remains to be deposited into the same watershed, but the airshed deposits much of the NOx along the U.S. eastern seaboard, including Chesapeake Bay, which also has a hypoxia problem. Most of the volatilized ammonia is produced from fertilizers or manure within the upper Mississippi River watershed, is deposited within a localized airshed, and is not airborne long distances like the NOx. The atmospheric nitrogen input to the coastal waters affected by hypoxia is considered to be minimal. In the last half century, the nitrogen load from the Mississippi River to the Gulf of Mexico has increased 300 percent. During this period, low oxygen bottom-waters have developed in the coastal waters and worsened coincident with the increase in the nitrogen load. The 31-yr average size of the bottom-water hypoxia area in the Gulf of Mexico is 13,800 square kilometers, well over the 5,000 square kilometers goal of the Mississippi River Nutrient/Gulf of Mexico Hypoxia Task Force. Knowing the amounts and sources of excess nutrients to watersheds with adjacent coastal waters experiencing eutrophication and hypoxia is important in the management strategies to reduce those nutrients and improve water quality.

A 22,000 year record of changing redox conditions from the Peruvian Oxygen Minimum Zone (OMZ): benthic foraminifera approach

NASA Astrophysics Data System (ADS)

Erdem, Z.; Schönfeld, J.; Glock, N.

2015-12-01

Benthic foraminifera have been used as proxies for the prevailing conditions at the sediment-water interface. Their distribution patterns are thought to facilitate reconstruction of past environmental conditions. Variations of bottom water oxygenation can be traced by the downcore distribution of benthic foraminifera and some of their morphological characters. Being one of the strongest and most pronounced OMZs in today's world oceans, the Peruvian OMZ is a key area to study such variations in relation with changing climate. Spatial changes or an extension of the OMZ through time and space are investigated using sediment cores from the lower OMZ boundary. We focus on time intervals Late Holocene, Early Holocene, Bølling Allerød, Heinrich-Stadial 1 and Last Glacial Maximum (LGM) to investigate changes in bottom-water oxygen and redox conditions. The recent distributions of benthic foraminiferal assemblages provide background data for an interpretation of the past conditions. Living benthic foraminiferal faunas from the Peruvian margin are structured with the prevailing bottom-water oxygen concentrations today (Mallon et al., 2012). Downcore distribution of benthic foraminiferal assemblages showed fluctuations in the abundance of the indicator species depicting variations and a decreasing trend in bottom water oxygen conditions since the LGM. In addition, changes in bottom-water oxygen and nitrate concentrations are reconstructed for the same time intervals by the pore density in tests of Planulina limbata and Bolivina spissa (Glock et al., 2011), respectively. The pore densities also indicate a trend of higher oxygen and nitrate concentrations in the LGM compared to the Holocene. Combination of both proxies provide information on past bottom-water conditions and changes of oxygen concentrations for the Peruvian margin. Glock et al., 2011: Environmental influences on the pore density of Bolivina spissa (Cushman), Journal of Foraminiferal Research, v. 41, no. 1, p. 22-32. Mallon et al., 2012: The response of benthic foraminifera to low-oxygen conditions of the Peruvian oxygen minimum zone, in ANOXIA, pp.305-322.

The tufas of Pyramid Lake, Nevada

USGS Publications Warehouse

Benson, Larry V.

2004-01-01

Pyramid Lake is the site of some of the Earth's most spectacular tufa deposits. The Tufas are composed of calcium carbonate (CaCO3). The large tufa mounds, reef- and sheet-like tufas formed within Pyramid Lake, between 26,000 and 13,000 years (yr) ago, when the lake was part of pluvial Lake Lahontan. The mounds are composed of large interlocking spheres that contain multiple generations of a crystalline (thinolite) variety of tufa. Over time many of the mounds have fallen apart, exposing an internal network of tubes. The tubular structures are thought to have been created when springs discharged from the bottom of Pyramid Lake, supplying calcium that combined with carbonate dissolved in lake water to form the mounds. The reef- and sheet-like deposits contain pillow and pendant forms made up of a branching variety of tufa that often grades into dense layers or nodules. Dense layers of tufa also coat cobbles and boulders that were deposited in near-shore shallow-water areas. The thickest tufa deposits formed at lake-bottom sites of ground-water discharge and at overflow elevations1 where the lake was held at near-constant levels for long periods of time.

Effects of hypolimnetic oxygen addition on mercury bioaccumulation in Twin Lakes, Washington, USA.

PubMed

Beutel, Marc; Dent, Stephen; Reed, Brandon; Marshall, Piper; Gebremariam, Seyoum; Moore, Barry; Cross, Benjamin; Gantzer, Paul; Shallenberger, Ed

2014-10-15

Twin Lakes, located on the Confederated Tribes of the Colville Indian Reservation in eastern Washington, USA, include North Twin Lake (NT) and South Twin Lake (ST). The mesotrophic, dimictic lakes are important recreational fishing sites for both warm-water bass and cold-water trout. To improve summertime cold-water habitat for trout in NT, dissolved oxygen (DO) addition to the hypolimnion, using liquid oxygen as an oxygen gas source, started in 2009. This study assessed mercury (Hg) in the water column, zooplankton and fish, and related water quality parameters, in Twin Lakes from 2009 to 2012. Because methylmercury (MeHg) buildup in lake bottom water is commonly associated with hypolimnetic anoxia, hypolimnetic oxygenation was hypothesized to reduce Hg in bottom waters and biota in NT relative to ST. Oxygen addition led to significantly higher DO (mean hypolimnetic DO: 2-8 mg/L versus <1 mg/L) and lower MeHg (peak mean hypolimnetic MeHg: 0.05-0.2 ng/L versus 0.15-0.4 ng/L) in North Twin. In North Twin, years with higher DO (2009 and 2011) exhibited lower MeHg in bottom waters and lower total Hg in zooplankton, inferring a positive linkage between oxygen addition and lower bioaccumulation. However, when comparing between the two lakes, Hg levels were significantly higher in zooplankton (total Hg range: 100-200 versus 50-100 μg/kg dry weight) and trout (spring 2010 stocking cohort of eastern brook trout mean total Hg: 74.9 versus 49.9 μg/kg wet weight) in NT relative to ST. Lower Hg bioaccumulation in ST compared to NT may be related to bloom dilution in chlorophyll-rich bottom waters, a vertical disconnect between the location of zooplankton and MeHg in the water column, and high binding affinity between sulfide and MeHg in bottom waters. Copyright © 2014 Elsevier B.V. All rights reserved.

Arsenic Movement From Sediment to Water: Microbes and Mobilization in a Contaminated Lake

NASA Astrophysics Data System (ADS)

Keimowitz, A. R.; Mailloux, B. J.; Chillrud, S. N.; Ross, J.; Wovkulich, K.; McNamara, P.; Alexandrova, E.; Thompson, L.

2008-12-01

Union Lake (Millville, NJ), a reservoir downstream from the Vineland Chemical Company Superfund site, has bottom sediments that are highly contaminated with arsenic (>1 g/kg). Offsite As transport was investigated. Because the lake is a result of damming, it is perched above the water table and therefore As transport may occur via downward movement of porewaters and/or groundwaters. Preliminary evidence for this was found in the form of iron flocculates enriched in As which were found in surface seeps downgradient of the dam. The possibility of As remobilization and/or off-site transport by seasonal anoxia of lake bottom- waters was also explored. Although historically, appreciable As was found in the water column of the lake (up to approximately 200 micrograms/L), As releases over the summers of 2007 and 2008 were negligible to modest with a maximum [As] of 23 micrograms/L. Arsenic mobilization from the contaminated sediments into surface waters of the reservoir are limited in part due to incomplete eutrophication and frequent overturning (approximately 1x/month in summer 2007) of this shallow lake, therefore conditions which promoted greater As release were explored in the laboratory. Field and laboratory samples were examined for changes in the microbial community using a variety of genetic techniques; these changes in microbial community were both a result of, and influenced, seasonal lake cycles.

Steel refining possibilities in LF

NASA Astrophysics Data System (ADS)

Dumitru, M. G.; Ioana, A.; Constantin, N.; Ciobanu, F.; Pollifroni, M.

2018-01-01

This article presents the main possibilities for steel refining in Ladle Furnace (LF). These, are presented: steelmaking stages, steel refining through argon bottom stirring, online control of the bottom stirring, bottom stirring diagram during LF treatment of a heat, porous plug influence over the argon stirring, bottom stirring porous plug, analysis of porous plugs disposal on ladle bottom surface, bottom stirring simulation with ANSYS, bottom stirring simulation with Autodesk CFD.

Near-bottom currents over the continental slope in the Mid-Atlantic Bight

USGS Publications Warehouse

Csanady, G.T.; Churchill, J.H.; Butman, B.

1988-01-01

From a set of 28 current meter records we have found that near-bottom currents faster than 0.2 m s-1 occur frequently over the outer continental shelf of the Mid-Atlantic Bight (bottom depth <210 m) but very rarely (<1% of the time) between bottom depths of 500 m and 2 km over the slope. The rarity of strong near-bottom flow over the middle and lower slope allows the accumulation of fine-grained sediment and organic carbon in this region. Fast near-bottom currents which do occur over the slope are invariably associated with topographic waves, although it is often superimposed inertial oscillations which increase current speed above the level of 0.2 m s-1. Episodes of intense inertial oscillations occur randomly and last typically for 10-20 days. Their energy source is unknown. Topographic wave energy exhibits a slight, but statistically significant, minimum over the mid-slope. These waves appear irregularly and vary both along isobaths and in time. The irregularity is presumably a consequence of random topographic wave generation by Gulf Stream instability. The current regime within sea-floor depressions in the slope (canyons and gullies) is distinctly different from that of the open slope; most notable is the near absence of topographic wave motion within depressions. ?? 1988.

The formation of Greenland Sea Deep Water: double diffusion or deep convection?

NASA Astrophysics Data System (ADS)

Clarke, R. Allyn; Swift, James H.; Reid, Joseph L.; Koltermann, K. Peter

1990-09-01

An examination of the extensive hydrographic data sets collected by C.S.S. Hudson and F.S. Meteor in the Norwegian and Greenland Seas during February-June 1982 reveals property distributions and circulation patterns broadly similar to those seen in earlier data sets. These data sets, however, reveal the even stronger role played by topography, with evidence of separate circulation patterns and separate water masses in each of the deep basins. The high precision temperature, salinity and oxygen data obtained reveals significant differences in the deep and bottom waters found in the various basins of the Norwegian and Greenland Seas. A comparison of the 1982 data set with earlier sets shows that the renewal of Greenland Sea Deep Water must have taken place sometime over the last decade; however there is no evidence that deep convective renewal of any of the deep and bottom waters in this region was taking place at the time of the observations. The large-scale density fields, however, do suggest that deep convection to the bottom is most likely to occure in the Greenland Basin due to its deep cyclonic circulation. The hypothesis that Greenland Sea Deep Water (GSDW) is formed through dipycnal mixing processes acting on the warm salty core of Atlantic Water entering the Greenland Sea is examined. θ-S correlations and oxygen concentrations suggest that the salinity maxima in the Greenland Sea are the product of at least two separate mixing processes, not the hypothesized single mixing process leading to GSDW. A simple one-dimensional mixed layer model with ice growth and decay demonstrates that convective renewal of GSDW would have occurred within the Greenland Sea had the winter been a little more severe. The new GSDW produced would have only 0.003 less salt and less than 0.04 ml 1 -1 greater oxygen concentration than that already in the basin. Consequently, detection of whether new deep water has been produced following a winter cooling season could be difficult even with the best of modern accuracy.

Instrumenting free-swimming dolphins echolocating in open water.

PubMed

Martin, Stephen W; Phillips, Michael; Bauer, Eric J; Moore, Patrick W; Houser, Dorian S

2005-04-01

Dolphins within the Navy Marine Mammal Program use echolocation to effectively locate underwater mines. They currently outperform manmade systems at similar tasks, particularly in cluttered environments and on buried targets. In hopes of improving manmade mine-hunting sonar systems, two instrumentation packages were developed to monitor free-swimming dolphin motion and echolocation during open-water target detection tasks. The biosonar measurement tool (BMT) is carried by a dolphin and monitors underwater position and attitude while simultaneously recording echolocation clicks and returning echoes through high-gain binaural receivers. The instrumented mine simulator (IMS) is a modified bottom target that monitors echolocation signals arriving at the target during ensonification. Dolphin subjects were trained to carry the BMT in open-bay bottom-object target searches in which the IMS could serve as a bottom object. The instrumentation provides detailed data that reveal hereto-unavailable information on the search strategies of free-swimming dolphins conducting open-water, bottom-object search tasks with echolocation.

Instrumenting free-swimming dolphins echolocating in open water

NASA Astrophysics Data System (ADS)

Martin, Stephen W.; Phillips, Michael; Bauer, Eric J.; Moore, Patrick W.; Houser, Dorian S.

2005-04-01

Dolphins within the Navy Marine Mammal Program use echolocation to effectively locate underwater mines. They currently outperform manmade systems at similar tasks, particularly in cluttered environments and on buried targets. In hopes of improving manmade mine-hunting sonar systems, two instrumentation packages were developed to monitor free-swimming dolphin motion and echolocation during open-water target detection tasks. The biosonar measurement tool (BMT) is carried by a dolphin and monitors underwater position and attitude while simultaneously recording echolocation clicks and returning echoes through high-gain binaural receivers. The instrumented mine simulator (IMS) is a modified bottom target that monitors echolocation signals arriving at the target during ensonification. Dolphin subjects were trained to carry the BMT in open-bay bottom-object target searches in which the IMS could serve as a bottom object. The instrumentation provides detailed data that reveal hereto-unavailable information on the search strategies of free-swimming dolphins conducting open-water, bottom-object search tasks with echolocation. .

Detection of Animal Viruses in Coastal Seawater and Sediments

PubMed Central

De Flora, Silvio; De Renzi, Giuseppe P.; Badolati, Giuseppe

1975-01-01

Animal viruses, predominantly enteroviruses, were detected in shallow waters at bottom depths and in clastic marine sediments. Viruses accumulated in sandy and slimy deposits of the sea bottom near the shore and could be easily released into water by means of simple mechanical shaking. Images PMID:170859

Microbial diversity from chlorophyll maximum, oxygen minimum and bottom zones in the southwestern Atlantic Ocean

NASA Astrophysics Data System (ADS)

Medina-Silva, Renata; de Oliveira, Rafael R.; Pivel, Maria A. G.; Borges, Luiz G. A.; Simão, Taiz L. L.; Pereira, Leandro M.; Trindade, Fernanda J.; Augustin, Adolpho H.; Valdez, Fernanda P.; Eizirik, Eduardo; Utz, Laura R. P.; Groposo, Claudia; Miller, Dennis J.; Viana, Adriano R.; Ketzer, João M. M.; Giongo, Adriana

2018-02-01

Conspicuous physicochemical vertical stratification in the deep sea is one of the main forces driving microbial diversity in the oceans. Oxygen and sunlight availability are key factors promoting microbial diversity throughout the water column. Ocean currents also play a major role in the physicochemical stratification, carrying oxygen down to deeper zones as well as moving deeper water masses up towards shallower depths. Water samples within a 50-km radius in a pockmark location of the southwestern Atlantic Ocean were collected and the prokaryotic communities from different water depths - chlorophyll maximum, oxygen minimum and deep-sea bottom (down to 1355 m) - were described. At phylum level, Proteobacteria were the most frequent in all water depths, Cyanobacteria were statistically more frequent in chlorophyll maximum zone, while Thaumarchaeota were significantly more abundant in both oxygen minimum and bottom waters. The most frequent microorganism in the chlorophyll maximum and oxygen minimum zones was a Pelagibacteraceae operational taxonomic unit (OTU). At the bottom, the most abundant genus was the archaeon Nitrosopumilus. Beta diversity analysis of the 16S rRNA gene sequencing data uncovered in this study shows high spatial heterogeneity among water zones communities. Our data brings important contribution for the characterisation of oceanic microbial diversity, as it consists of the first description of prokaryotic communities occurring in different oceanic water zones in the southwestern Atlantic Ocean.

On influencing factors of hypoxia in waters adjacent to the Changjiang estuary

NASA Astrophysics Data System (ADS)

Luo, Xiaofan; Wei, Hao; Fan, Renfu; Liu, Zhe; Zhao, Liang; Lu, Youyu

2018-01-01

Based on observational data from ten cruises carried out in 2012 and 2013, the distribution of dissolved oxygen (DO) and the evolution of hypoxia (DO concentrations < 2.0 mg L-1) in waters adjacent to the Changjiang estuary are studied. The linkage between summer hypoxia and hydrodynamic conditions is explored. The results suggest that hypoxia frequently occurred from June to October to the south of the Changjiang estuary near the 30-50 m isobaths and was prone to happening under strong stratification without the presence of the Kuroshio Subsurface Water (KSW). Over the Changjiang Bank, hypoxia mainly occurred in July, August and September. Low-oxygen areas initially appeared under strong stratification induced by the spreading of the Changjiang Diluted Water (CDW), and developed into hypoxic zones due to lack of DO replenishment from the relatively DO-rich Yellow Sea Water and the KSW. The yearly evolution of hypoxia was influenced by shelf circulation especially the path of the KSW in the bottom layer of the water to the south of the Changjiang estuary, and the extension of the CDW in the surface layer over the Changjiang Bank.

Linear shoaling of free-surface waves in multi-layer non-hydrostatic models

NASA Astrophysics Data System (ADS)

Bai, Yefei; Cheung, Kwok Fai

2018-01-01

The capability to describe shoaling over sloping bottom is fundamental to modeling of coastal wave transformation. The linear shoaling gradient provides a metric to measure this property in non-hydrostatic models with layer-integrated formulations. The governing equations in Boussinesq form facilitate derivation of the linear shoaling gradient, which is in the form of a [ 2 P + 2 , 2 P ] expansion of the water depth parameter kd with P equal to 1 for a one-layer model and (4 N - 4) for an N-layer model. The expansion reproduces the analytical solution from Airy wave theory at the shallow water limit and maintains a reasonable approximation up to kd = 1.2 and 2 for the one and two-layer models. Additional layers provide rapid and monotonic convergence of the shoaling gradient into deep water. Numerical experiments of wave propagation over a plane slope illustrate manifestation of the shoaling errors through the transformation processes from deep to shallow water. Even though outside the zone of active wave transformation, shoaling errors from deep to intermediate water are cumulative to produce appreciable impact to the wave amplitude in shallow water.

Effect of bottom slope on the nonlinear triad interactions in shallow water

NASA Astrophysics Data System (ADS)

Chen, Hongzhou; Tang, Xiaocheng; Zhang, Ri; Gao, Junliang

2018-05-01

This paper aims at investigating the effect of bottom slope to the nonlinear triad interactions for irregular waves propagating in shallow water. The physical experiments are conducted in a wave flume with respect to the transformation of waves propagating on three bottom slopes ( β = 1/15, 1/30, and 1/45). Irregular waves with different type of breaking that are mechanically generated based on JONSWAP spectra are used for the test. The obviously different variations of spectra measured on each bottom reveal a crucial role of slope effect in the energy transfer between harmonics. The wavelet-based bispectrum were used to examine the bottom slope effect on the nonlinear triad interactions. Results show that the different bottom slopes which waves are propagated on will cause a significant discrepancy of triad interactions. Then, the discussions on the summed bicoherence which denote the distribution of phase coupling on each frequency further clarify the effect of bottom slope. Furthermore, the summed of the real and imaginary parts of bispectrum which could reflect the intensity of frequency components participating in the wave skewness and asymmetry were also investigated. Results indicate that the value of these parameters will increase as the bottom slope gets steeper.

An Improved Heat Budget Estimation Including Bottom Effects for General Ocean Circulation Models

NASA Technical Reports Server (NTRS)

Carder, Kendall; Warrior, Hari; Otis, Daniel; Chen, R. F.

2001-01-01

This paper studies the effects of the underwater light field on heat-budget calculations of general ocean circulation models for shallow waters. The presence of a bottom significantly alters the estimated heat budget in shallow waters, which affects the corresponding thermal stratification and hence modifies the circulation. Based on the data collected during the COBOP field experiment near the Bahamas, we have used a one-dimensional turbulence closure model to show the influence of the bottom reflection and absorption on the sea surface temperature field. The water depth has an almost one-to-one correlation with the temperature rise. Effects of varying the bottom albedo by replacing the sea grass bed with a coral sand bottom, also has an appreciable effect on the heat budget of the shallow regions. We believe that the differences in the heat budget for the shallow areas will have an influence on the local circulation processes and especially on the evaporative and long-wave heat losses for these areas. The ultimate effects on humidity and cloudiness of the region are expected to be significant as well.

The comparative limnology of Lakes Nyos and Monoun, Cameroon

USGS Publications Warehouse

Kling, George; Evans, William C; Tanyileke, Gregory

2015-01-01

Lakes Nyos and Monoun are known for the dangerous accumulation of CO2 dissolved in stagnant bottom water, but the shallow waters that conceal this hazard are dilute and undergo seasonal changes similar to other deep crater lakes in the tropics. Here we discuss these changes with reference to climatic and water-column data collected at both lakes during the years following the gas release disasters in the mid-1980s. The small annual range in mean daily air temperatures leads to an equally small annual range of surface water temperatures (ΔT ~6–7 °C), reducing deep convective mixing of the water column. Weak mixing aids the establishment of meromixis, a requisite condition for the gradual buildup of CO2 in bottom waters and perhaps the unusual condition that most explains the rarity of such lakes. Within the mixolimnion, a seasonal thermocline forms each spring and shallow diel thermoclines may be sufficiently strong to isolate surface water and allow primary production to reduce PCO2 below 300 μatm, inducing a net influx of CO2 from the atmosphere. Surface water O2 and pH typically reach maxima at this time, with occasional O2 oversaturation. Mixing to the chemocline occurs in both lakes during the winter dry season, primarily due to low humidity and cool night time air temperature. An additional period of variable mixing, occasionally reaching the chemocline in Lake Monoun, occurs during the summer monsoon season in response to increased frequency of major storms. The mixolimnion encompassed the upper ~40–50 m of Lake Nyos and upper ~15–20 m of Lake Monoun prior to the installation of degassing pipes in 2001 and 2003, respectively. Degassing caused chemoclines to deepen rapidly. Piping of anoxic, high-TDS bottom water to the lake surface has had a complex effect on the mixolimnion. Algal growth stimulated by increased nutrients (N and P) initially stimulated photosynthesis and raised surface water O2 in Lake Nyos, but O2 removal through oxidation of iron was also enhanced and appeared to dominate at Lake Monoun. Depth-integrated O2 contents decreased in both lakes as did water transparency. No dangerous instabilities in water-column structure were detected over the course of degassing. While Nyos-type lakes are extremely rare, other crater lakes can pose dangers from gas releases and monitoring is warranted.

Insecticide residues on stream sediments in Ontario, Canada.

PubMed

Miles, J R

1976-12-01

Insecticide residues on suspended and bottom sediments of streams of Ontario, Canada, have been studied in a tobacco-growing and a vegetable muck area. The proportion of TDE to DDT was less than 1 in water and greater than 1 in bottom sediments. The ratio of TDE to DDT in bottom material increased linearly from the contamination point at stream source to the mouth of Big Creek in Norfolk County, Ontario. Bed load samples contained three to six times greater concentrations of insecticides than bottom material. Adsorption of insecticides on suspended sediment decreased in order DDT greater than TDE greater than dieldrin greater than diazinon, which is consistent with the water solubility of these compounds.

Water depth measurement using an airborne pulsed neon laser system

NASA Technical Reports Server (NTRS)

Hoge, F. E.; Swift, R. N.; Frederick, E. B.

1980-01-01

The paper presents the water depth measurement using an airborne pulsed neon laser system. The results of initial base-line field test results of NASA airborne oceanographic lidar in the bathymetry mode are given, with water-truth measurements of depth and beam attenuation coefficients by boat taken at the same time as overflights to aid in determining the system's operational performance. The nadir-angle tests and field-of-view data are presented; this laser bathymetry system is an improvement over prior models in that (1) the surface-to-bottom pulse waveform is digitally recorded on magnetic tape, and (2) wide-swath mapping data may be routinely acquired using a 30 deg full-angle conical scanner.

Experimental and theoretical modelling of sand-water-object interaction under nonlinear progressive waves

NASA Astrophysics Data System (ADS)

Testik, Firat Yener

An experimental and theoretical study has been conducted to obtain a fundamental understanding of the dynamics of the sand, water and a solid object interaction as progressive gravity waves impinge on a sloping beach. Aside from obvious scientific interest, this exceedingly complex physical problem is important for naval applications, related to the behavior of disk/cylindrical shaped objects (mines) in the coastal waters. To address this problem, it was divided into a set of simpler basic problems. To begin, nonlinear progressive waves were investigated experimentally in a wave tank for the case of a rigid (impermeable) sloping bottom. Parameterizations for wave characteristics were proposed and compared with the experiments. In parallel, a numerical wave tank model (NWT) was calibrated using experimental data from a single run, and wave field in the wave tank was simulated numerically for the selected experiments. Subsequently, a layer of sand was placed on the slope and bottom topography evolution processes (ripple and sandbar dynamics, bottom topography relaxation under variable wave forcing, etc.) were investigated experimentally. Models for those processes were developed and verified by experimental measurements. Flow over a circular cylinder placed horizontally on a plane wall was also studied. The far-flow field of the cylinder placed in the wave tank was investigated experimentally and numerical results from the NWT simulations were compared with the experimental data. In the mean time, the near-flow velocity/vorticity field around a short cylinder under steady and oscillatory flow was studied in a towing tank. Horseshoe vortex formation and periodic shedding were documented and explained. With the understanding gained through the aforementioned studies, dynamics and burial/scour around the bottom objects in the wave tank were studied. Possible scenarios on the behavior of the disk-shaped objects were identified and explained. Scour around 3D cylindrical objects was investigated. Different scour regimes were identified experimentally and explained theoretically. Proper physical parameterizations on the time evolution and equilibrium scour characteristics were proposed and verified experimentally.

Bottom water production variability in the Ross Sea slope during the Late Pleistocene-Holocene as revealed by benthic foraminifera and sediment geochemistry

NASA Astrophysics Data System (ADS)

Langone, Leonardo; Asioli, Alessandra; Tateo, Fabio; Giglio, Federico; Ridente, Domenico; Summa, Vito; Carraro, Anna; Luigia Giannossi, Maria; Piva, Andrea; Trincardi, Fabio

2010-05-01

The Antarctic area produces bottom waters that ventilate the vast majority of the deep basins in the rest of the world ocean. The rate of formation in the source area and the strength of these cold bottom waters are key factors affecting the Global Thermohaline Circulation during modern and past climate conditions. The western Ross Sea is considered a formation site for a particularly salty variety of AABW as well as an important area of off-shelf transfer of water as plumes entraining in Lower CDW and as rapid downhill cascades. The results here presented were obtained within the frame of the PNRA project 4.8. Among the goals of the project, the main is to detect a qualitative signal of possible changes in the rate of bottom water production during the Late Pleistocene-Holocene by integrating data on foraminifera assemblages with sediment geochemistry (bulk mineralogy, Total Organic Carbon, biogenic silica, C and N stable isotopes) and IRD. A gravity core was collected at 2377m water depth off Drygalski Basin on the slope adjacent the western continental shelf of the Ross Sea, along the pathway of bottom water spreading. The chronology is based on the best fitting of twelve control points selected among twenty-two 14C AMS datings performed on the bulk organic carbon and 210Pb excess data. The trend of the parameters allows the following observations: 1) two main intervals (15-10 and 7.5-6 cab kyr BP) mark a subsequent enhanced nutrient supply. Indeed, δ15N variations depend on the utilization degree of nitrates, in turn reflecting productivity/nutrient supply changes. The concurrent increase of OC and biogenic silica suggests an increase of the nutrient availability. As the Upper CDW is a water mass rich in nutrients we interpret these intervals as characterized by a higher efficiency in the Upper CDW upwelling; 2) around 7.5-7kyr BP (part of the Middle Holocene Climatic Optimum) the IRD content drops, suggesting the reduction of iceberg production or a change of the iceberg path. Within this general context, an oscillatory trend is present from 15 kyr BP to present time. Two hypotheses are proposed: a) minima in foraminifera concentrations reflect relatively stronger dissolution, weaker bottom currents (minima in dry density) and lower nutrient supply (lighter values of δ15N). These intervals may reflect a lower rate of bottom water formation; the intervals corresponding to maxima in foraminifers concentration should indicate better preservation, higher benthic productivity and/or better oxygenation at bottom, stronger bottom currents (maxima in dry density) and relatively higher nutrient supply reflecting a relatively higher rate of bottom water formation. b) alternatively, minima in foraminifers, corresponding to minima in %OC and to reversal of 14C (relative increase of older carbon), reflect dilution in the sediment because of rapid accumulation of fine sediment re-suspended at the shelf edge by the cascading currents. Therefore, the minima represent higher rate of bottom water formation. The comparison of the D/H ratio in ice-cores from the Ross Sea sector with the core AS05-10 record indicates that the foraminifers minima always correspond to colder condition. This scenario also correlates to the record reported in literature on the slope off Wilkes-Adelie Land. At last, a condensed/hiatus interval at ca. 3.5-4 kyr BP does not seems to mark a major change in the general pattern of our variables, apart from biogenic silica and sheets silicates showing an increase of the oscillation amplitude. Nevertheless, this feature is coeval to the base of the Neoglacial and it is time-equivalent to the beginning of major changes in the Antarctic environment.

The Structure of Microbial Community and Degradation of Diatoms in the Deep Near-Bottom Layer of Lake Baikal

PubMed Central

Zakharova, Yulia R.; Galachyants, Yuri P.; Kurilkina, Maria I.; Likhoshvay, Alexander V.; Petrova, Darya P.; Shishlyannikov, Sergey M.; Ravin, Nikolai V.; Mardanov, Andrey V.; Beletsky, Alexey V.; Likhoshway, Yelena V.

2013-01-01

Insight into the role of bacteria in degradation of diatoms is important for understanding the factors and components of silica turnover in aquatic ecosystems. Using microscopic methods, it has been shown that the degree of diatom preservation and the numbers of diatom-associated bacteria in the surface layer of bottom sediments decrease with depth; in the near-bottom water layer, the majority of bacteria are associated with diatom cells, being located either on the cell surface or within the cell. The structure of microbial community in the near-bottom water layer has been characterized by pyrosequencing of the 16S rRNA gene, which has revealed 149 208 unique sequences. According to the results of metagenomic analysis, the community is dominated by representatives of Proteobacteria (41.9%), Actinobacteria (16%); then follow Acidobacteria (6.9%), Cyanobacteria (5%), Bacteroidetes (4.7%), Firmicutes (2.8%), Nitrospira (1.6%), and Verrucomicrobia (1%); other phylotypes account for less than 1% each. For 18.7% of the sequences, taxonomic identification has been possible only to the Bacteria domain level. Many bacteria identified to the genus level have close relatives occurring in other aquatic ecosystems and soils. The metagenome of the bacterial community from the near-bottom water layer also contains 16S rRNA gene sequences found in previously isolated bacterial strains possessing hydrolytic enzyme activity. These data show that potential degraders of diatoms occur among the vast variety of microorganisms in the near-bottom water of Lake Baikal. PMID:23560063

Comparision of Bathymetry and Bottom Characteristics From Hyperspectral Remote Sensing Data and Shipborne Acoustic Measurements

NASA Astrophysics Data System (ADS)

McIntyre, M. L.; Naar, D. F.; Carder, K. L.; Howd, P. A.; Lewis, J. M.; Donahue, B. T.; Chen, F. R.

2002-12-01

There is growing interest in applying optical remote sensing techniques to shallow-water geological applications such as bathymetry and bottom characterization. Model inversions of hyperspectral remote-sensing reflectance imagery can provide estimates of bottom albedo and depth. This research was conducted in support of the HyCODE (Hyperspectral Coupled Ocean Dynamics Experiment) project in order to test optical sensor performance and the use of a hyperspectral remote-sensing reflectance algorithm for shallow waters in estimating bottom depths and reflectance. The objective of this project was to compare optically derived products of bottom depths and reflectance to shipborne acoustic measurements of bathymetry and backscatter. A set of three high-resolution, multibeam surveys within an 18 km by 1.5 km shore-perpendicular transect 5 km offshore of Sarasota, Florida were collected at water depths ranging from 8 m to 16 m. These products are compared to bottom depths derived from aircraft remote-sensing data collected with the AVIRIS (Airborne Visible-Infrared Imaging Spectrometer) instrument data by means of a semi-analytical remote sensing reflectance model. The pixel size of the multibeam bathymetry and AVIRIS data are 0.25 m and 10 m, respectively. When viewed at full resolution, the multibeam bathymetry data show small-scale sedimentary bedforms (wavelength ~10m, amplitude ~1m) that are not observed in the lower resolution hyperspectral bathymetry. However, model-derived bottom depths agree well with a smoothed version of the multibeam bathymetry. Depths derived from shipborne hyperspectral measurements were accurate within 13%. In areas where diver observations confirmed biological growth and bioturbation, derived bottom depths were less accurate. Acoustic backscatter corresponds well with the aircraft hyperspectral imagery and in situ measurements of bottom reflectance. Acoustic backscatter was used to define the distribution of different bottom types. Acoustic backscatter imagery corresponds well with the AVIRIS data in the middle to outer study area, implying a close correspondence between seafloor character and optical reflectance. AVIRIS data in the inner study area show poorer correspondence with the acoustic facies, indicating greater water column effects (turbidity). Acoustic backscatter as a proxy for bottom albedo, in conjunction with multibeam bathymetry data, will allow for more precise modeling of the optical signal in coastal environments.

A numerical study of circulation driven by mixing over a submarine bank

NASA Astrophysics Data System (ADS)

Cummins, Patrick F.; Foreman, Michael G. G.

1998-04-01

A primitive equation model is applied to study the spin-up of a linearly stratified, rotating fluid over an isolated topographic bank. The model has vertical eddy mixing coefficients that decay away from the bottom over a specified e-folding scale. No external flows are imposed, and a circulation develops due solely to diffusion over the sea bed. Vertical mixing, coupled with the condition of zero diffusive flux of heat through the sea floor, leads to a distortion of isothermal surfaces near the bottom. The associated radial pressure gradients drive a radial-overturning circulation with upslope flow just above the bottom and downslope flows at greater height. Coriolis forces on the radial flows accelerate a verticallysheared azimuthal (alongslope) circulation. Near the bottom the azimuthal motion is cyclonic (upwelling favourable), while outside the boundary layer, the motion is anticyclonic. Sensitivity experiments show that this pattern is robust and maintained even with constant mixing coefficients. Attention is given to the driving mechanism for the depth-averaged azimuthal motion. An analysis of the relative angular momentum balance determines that the torque associated with bottom stresses drives the anticyclonic depth-averaged flow. In terms of vorticity, the anticyclonic vortex over the bank arises due to the curl of bottom stress divided by the depth. A parameter sensitivity study indicates that the depth-averaged flow is relatively insensitive to variations in the bottom drag coefficient.

The spatial and temporal distribution of chemical species in Padaviya Reservoir, Sri Lanka.

NASA Astrophysics Data System (ADS)

Koliyabandara, S. M. P. A.; Siriwardhana, C.; Cooray, P. L. A. T.; Liyanage, S. S.

2017-12-01

Water is one of the most important assets for human life. Eutrophication and pollution are some of the major threats to many freshwater bodies. There are thousands of reservoirs exist in Sri Lanka; however, only a handful of them has been thoroughly monitored and studied. The main objective of this study is to investigate the temporal and spatial distribution of chemical species in Padaviya reservoir which is shallow man-made irrigation reservoir (8°49'30.6" N and 80°46'2.05"E) located in Sri Lanka constructed around 300 BC. The average depth is 8 m and 4 m in wet and dry seasons respectively. It has a catchment area of 270 km2. Water sampling was done at bi-monthly intervals for a period of one year staring from January 2016. Chemical analyses were conducted according to standard protocols. The maximum temperature difference between the surface and bottom waters of the reservoir was 2 °C throughout the year. The surface and bottom water conductivity varied between 175 ± 2.3 to 250 ± 3.0 μS cm-1 and 475 ± 3.7 to 600 ± 4.5 μScm-1 respectively. The average pH of surface and bottom waters varied between 8.5 ± 0.1 to 7.8 ± 0.2 and 7.2 ± 0.02 to 6.8 ± 0.2 respectively. The dissolved oxygen concentration showed a clinograde type distribution throughout the year where the surface waters were well oxygenated (DO ≈ 7.5 ppm) and the bottom waters were anoxic (DO ≈ 0.15 ppm). Ammonia concentration increased with the depth from surface concentration of 150 ± 50 to 300 ± 25 ppb at the bottom. Nitrite distribution was similar to ammonia and the surface concentration was 100 ± 25ppb throughtout the year and at the bottom it varied between 300 ± 30 to 4500 ± 30 ppb. Water soluble phosphate distribution was also similar to ammonia. The surface concentration was 200 ± 20 ppb throughtout the year and varied from 100 ± 20 to 2000 ±20 ppb at the bottom. Nitrate distribution was inverse of the ammonia. The surface concentration was 500 ± 30 to 900 ± 30 ppb while the it was 100 ± 30ppb at the bottom throughout the year. The fluctionations of the concentrations of chemical species was attributed to the wet and dry seasons of the reservoir. Key words - Chemical species, Water quality, Padaviya,Acknowledgement - Financial support by University of Sri Jayewardenepura, ASP/01/RE/SCI/2015/29.

Using oxygen isotopes to establish freshwater sources in Bedford Basin, Nova Scotia, a Northwestern Atlantic fjord

NASA Astrophysics Data System (ADS)

Kerrigan, Elizabeth A.; Kienast, Markus; Thomas, Helmuth; Wallace, Douglas W. R.

2017-12-01

A weekly time-series of oxygen isotope (δ18O) measurements was collected over a 16-month period from near-surface (1 m) and near-bottom (60 m) waters of Bedford Basin, a coastal fjord adjacent to the Scotian Shelf, off eastern Canada. The time-series was complemented with δ18O measurements of local precipitation (rain and snow), river, and wastewater runoff. The isotopic composition of precipitation displayed strong seasonality with an average (volume-weighted) δ18O value of -5.39‰ (±0.96) for summer and a depleted value of -10.37‰ (±2.96) over winter. Winter precipitation exhibited more depleted and variable δ18O of solid precipitation relative to rainfall. The annual, amount-weighted average δ18O of Sackville River discharge (-6.49‰ ± 0.82) was not statistically different from precipitation (-7.24‰ ± 0.92), but exhibited less seasonal variation. Freshwater end-members (zero-salinity intercepts) estimated from annual and seasonal regressions of δ18O versus salinity (S) for Bedford Basin near-surface samples were consistent with the δ18O of summer precipitation and the annual, amount-weighted average for the Sackville River. However, the isotopically depleted signature of winter precipitation was not observed clearly in near-surface waters of Bedford Basin, which might reflect isotope enrichment during sublimation from accumulated snowfall prior to melting and discharge, or retention and mixing within the drainage basin. In near bottom waters, most of the δ18O-S variation (average freshwater end-member: 7.47‰ ± 2.17) could be explained by vertical mixing with near-surface waters (average freshwater end-member: -6.23‰ ± 0.34) and hence with locally-derived freshwater. However the near-bottom δ18O-S variation suggested an additional contribution of a freshwater end-member with a δ18O of -15.55‰ ± 2.3, consistent with a remotely-derived freshwater end-member identified previously for the Scotian Shelf. Residuals from a long-term regression of δ18O-S were generally within the range expected due to analytical uncertainty (±0.05); however near-surface waters exhibited seasonal variability of small amplitude, which was consistent with the timing and δ18O variability of local freshwater inputs.

Acceptance test report, 241-SY-101 Flexible Receiver System, Phase 2 testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ritter, G.A.

1995-02-06

This document summarizes the results of the Phase 2 acceptance test of the 241-SY-101 Flexible Receiver System (FRS). The FRS is one of six major components of the Equipment Removal System, which has been designed to retrieve, transport, and store the test mixer pump currently installed in Tank 241-SY-101. The purpose of this acceptance test is to verify the strength of the containment bag and bag bottom cinching mechanism. It is postulated that 68 gallons of waste could be trapped inside the pump internals. The bag must be capable of supporting this waste if it shakes loose and drains tomore » the bottom of the bag after the bag bottom has been cinched closed. This acceptance test was performed at the Maintenance and Storage Facility (MASF) Facility in the 400 area on January 23, 1995. The bag assembly supported the weight of 920 kg (2,020 lbs) of water with no leakage or damage to the bag. This value meets the acceptance criteria of 910 kg of water and therefore the results were found to be acceptable. The maximum volume of liquid expected to be held up in the pump internals is 258 L (68 gallons), which corresponds to 410 kg. This test weight gives just over a safety factor of 2. The bag also supported a small shock load while it was filled with water when the crane hoisted the bag assembly up and down. Based on the strength rating of the bag components, the bag assembly should support 2--3 times the test weight of 910 kg.« less

Can biophysical properties of submersed macrophytes be determined by remote sensing?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malthus, T.J.; Ciraolo, G.; La Loggia, G.

1997-06-01

This paper details the development of a computationally efficient Monte Carlo simulation program to model photon transport through submersed plant canopies, with emphasis on Seagrass communities. The model incorporates three components: the transmission of photons through a water column of varying depth and turbidity; the interaction of photons within a submersed plant canopy of varying biomass; and interactions with the bottom substrate. The three components of the model are discussed. Simulations were performed based on measured parameters for Posidonia oceanica and compared to measured subsurface reflectance spectra made over comparable seagrass communities in Sicilian coastal waters. It is shown thatmore » the output is realistic. Further simulations are undertaken to investigate the effect of depth and turbidity of the overlying water column. Both sets of results indicate the rapid loss of canopy signal as depth increases and water column phytoplankton concentrations increase. The implications for the development of algorithms for the estimation of submersed canopy biophysical parameters are briefly discussed.« less

Factors controlling bacteria and protists in selected Mazurian eutrophic lakes (North-Eastern Poland) during spring

PubMed Central

2013-01-01

Background The bottom-up (food resources) and top-down (grazing pressure) controls, with other environmental parameters (water temperature, pH) are the main factors regulating the abundance and structure of microbial communities in aquatic ecosystems. It is still not definitively decided which of the two control mechanisms is more important. The significance of bottom-up versus top-down controls may alter with lake productivity and season. In oligo- and/or mesotrophic environments, the bottom-up control is mostly important in regulating bacterial abundances, while in eutrophic systems, the top-down control may be more significant. Results The abundance of bacteria, heterotrophic (HNF) and autotrophic (ANF) nanoflagellates and ciliates, as well as bacterial production (BP) and metabolically active cells of bacteria (CTC, NuCC, EST) were studied in eutrophic lakes (Mazurian Lake District, Poland) during spring. The studied lakes were characterized by high nanoflagellate (mean 17.36 ± 8.57 × 103 cells ml-1) and ciliate abundances (mean 59.9 ± 22.4 ind. ml-1) that were higher in the euphotic zone than in the bottom waters, with relatively low bacterial densities (4.76 ± 2.08 × 106 cells ml-1) that were lower in the euphotic zone compared to the profundal zone. Oligotrichida (Rimostrombidium spp.), Prostomatida (Urotricha spp.) and Scuticociliatida (Histiobalantium bodamicum) dominated in the euphotic zone, whereas oligotrichs Tintinnidium sp. and prostomatids Urotricha spp. were most numerous in the bottom waters. Among the staining methods used to examine bacterial cellular metabolic activity, the lowest percentage of active cells was recorded with the CTC (1.5–15.4%) and EST (2.7–14.2%) assay in contrast to the NuCC (28.8–97.3%) method. Conclusions In the euphotic zone, the bottom-up factors (TP and DOC concentrations) played a more important role than top-down control (grazing by protists) in regulating bacterial numbers and activity. None of the single analyzed factors controlled bacterial abundance in the bottom waters. The results of this study suggest that both control mechanisms, bottom-up and top-down, simultaneously regulated bacterial community and their activity in the profundal zone of the studied lakes during spring. In both lake water layers, food availability (algae, nanoflagellates) was probably the major factor determining ciliate abundance and their composition. In the bottom waters, both groups of protists appeared to be also influenced by oxygen, temperature, and total phosphorus. PMID:23566491

Chemical quality of water and bottom sediment, Stillwater National Wildlife Refuge, Lahontan Valley, Nevada

USGS Publications Warehouse

Thodal, Carl E.

2017-12-28

The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service collected data on water and bottom-sediment chemistry to be used to evaluate a new water rights acquisition program designed to enhance wetland habitat in Stillwater National Wildlife Refuge and in Lahontan Valley, Churchill County, Nevada. The area supports habitat critical to the feeding and resting of migratory birds travelling the Pacific Flyway. Information about how water rights acquisitions may affect the quality of water delivered to the wetlands is needed by stakeholders and Stillwater National Wildlife Refuge managers in order to evaluate the effectiveness of this approach to wetlands management. A network of six sites on waterways that deliver the majority of water to Refuge wetlands was established to monitor the quality of streamflow and bottom sediment. Each site was visited every 4 to 6 weeks and selected water-quality field parameters were measured when flowing water was present. Water samples were collected at varying frequencies and analyzed for major ions, silica, and organic carbon, and for selected species of nitrogen and phosphorus, trace elements, pharmaceuticals, and other trace organic compounds. Bottom-sediment samples were collected for analysis of selected trace elements.Dissolved-solids concentrations exceeded the recommended criterion for protection of aquatic life (500 milligrams per liter) in 33 of 62 filtered water samples. The maximum arsenic criterion (340 micrograms per liter) was exceeded twice and the continuous criterion was exceeded seven times. Criteria protecting aquatic life from continuous exposure to aluminum, cadmium, lead, and mercury (87, 0.72, 2.5, and 0.77 micrograms per liter, respectively) were exceeded only once in filtered samples (27, 40, 32, and 36 samples, respectively). Mercury was the only trace element analyzed in bottom-sediment samples to exceed the published probable effect concentration (1,060 micrograms per kilogram).

Evaluation of organic compounds and trace elements in Amazon Creek Basin, Oregon, September 1990

USGS Publications Warehouse

Rinella, F.A.

1993-01-01

Water and bottom sediment were collected from Amazon Creek, Oregon during a summer low-flow condition and analyzed for different classes of organic compounds, including many from the U.S. Environmental Protection Agency's priority pollutant list. Bottom sediment also was analyzed for trace elements typically associated with urban runoff. Trace-element concentrations in the less than 63 micrometer fraction of Amazon Creek bottom-sediment samples were compared with baseline concentrations (expected 95 percent confidence range) for soils from the Western United States and with concen- trations found in bottom sediment from the Willamette River Basin. Total-digestion concentrations of antimony, arsenic, cadmium, chromium, cobalt, copper, lead, manganese, mercury, nickel, silver, titanium, and zinc were enriched at some or all sites sampled. Whole-water samples from some sites contained concentrations of several chlorophenoxy-acid herbicides, the organophosphorus insecticide diazinon, and several semivolatile priority pollutants. Classes of compounds not detected in whole-water samples included carbamate insecticides, triazine and other nitrogen-containing herbicides, and purgeable organic compounds. Bottom-sediment samples contained many organochlorine compounds, including chlordane, DDT plus metabolites, dieldrin, endrin, heptachlor epoxide (a metabolite of heptachlor), and PCBs at some or all sites sampled. Twenty-four of 54 semivolatile compounds were detected in bottom- sediment samples at some or all sites sampled.

Possible Significance of Early Paleozoic Fluctuations in Bottom Current Intensity, Northwest Iapetus Ocean

NASA Astrophysics Data System (ADS)

Lash, Gary G.

1986-06-01

Sedimentologic and geochemical characteristics of red and green deep water mudstone exposed in the central Appalachian orogen define climatically-induced fluctuations in bottom current intensity along the northwest flank of the Iapetus Ocean in Early and Middle Ordovician time. Red mudstone accumulated under the influence of moderate to vigorous bottom current velocities in oxygenated bottom water produced during climatically cool periods. Interbedded green mudstone accumulated at greater sedimentation rates, probably from turbidity currents, under the influence of reduced thermohaline circulation during global warming periods. The close association of green mudstone and carbonate turbidites of Early Ordovician (late Tremadocian to early Arenigian) age suggests that a major warming phase occurred at this time. Increasing temperatures reduced bottom current velocities and resulted in increased production of carbonate sediment and organic carbon on the carbonate platform of eastern North America. Much of the excess carbonate sediment and organic carbon was transported into deep water by turbidity currents. Although conclusive evidence is lacking, this eustatic event may reflect a climatic warming phase that followed the postulated glacio-eustatic Black Mountain event. Subsequent Middle Ordovician fluctuations in bottom current intensity recorded by thin red-green mudstone couplets probably reflect periodic growth and shrinkage of an ice cap rather than major glacial episodes.

Passive thermal refugia provided warm water for Florida manatees during the severe winter of 2009-2010

USGS Publications Warehouse

Stith, B.M.; Slone, D.H.; de Wit, M.; Edwards, H.H.; Langtimm, C.A.; Swain, E.D.; Soderqvist, L.E.; Reid, J.P.

2012-01-01

Haloclines induced by freshwater inflow over tidal water have been identified as an important mechanism for maintaining warm water in passive thermal refugia (PTR) used by Florida manatees Trichechus manatus latirostris during winter in extreme southwestern Florida. Record-setting cold during winter 2009–2010 resulted in an unprecedented number of manatee deaths, adding to concerns that PTR may provide inadequate thermal protection during severe cold periods. Hydrological data from 2009–2010 indicate that 2 canal systems in the Ten Thousand Islands (TTI) region acted as PTR and maintained warm bottom-water temperatures, even during severe and prolonged cold periods. Aerial survey counts of live and dead manatees in TTI during the winter of 2009–2010 suggest that these PTR were effective at preventing mass mortality from hypothermia, in contrast to the nearby Everglades region, which lacks similar artificial PTR and showed high manatee carcass counts. Hydrological data from winter 2008–2009 confirmed earlier findings that without haloclines these artificial PTR may become ineffective as warm-water sites. Tidal pumping of groundwater appears to provide additional heat to bottom water during low tide cycles, but the associated thermal inversion is not observed unless salinity stratification is present. The finding that halocline-driven PTR can maintain warm water even under extreme winter conditions suggests that they may have significant potential as warm-water sites. However, availability and conflicting uses of freshwater and other management issues may make halocline-driven PTR unreliable or difficult to manage during winter.

Plio-Pleistocene evolution of water mass exchange and erosional input at the Atlantic-Arctic gateway

NASA Astrophysics Data System (ADS)

Teschner, Claudia; Frank, Martin; Haley, Brian A.; Knies, Jochen

2016-05-01

Water mass exchange between the Arctic Ocean and the Norwegian-Greenland Seas has played an important role for the Atlantic thermohaline circulation and Northern Hemisphere climate. We reconstruct past water mass mixing and erosional inputs from the radiogenic isotope compositions of neodymium (Nd), lead (Pb), and strontium (Sr) at Ocean Drilling Program site 911 (leg 151) from 906 m water depth on Yermak Plateau in the Fram Strait over the past 5.2 Myr. The isotopic compositions of past bottom waters were extracted from authigenic oxyhydroxide coatings of the bulk sediments. Neodymium isotope signatures obtained from surface sediments agree well with present-day deepwater ɛNd signature of -11.0 ± 0.2. Prior to 2.7 Ma the Nd and Pb isotope compositions of the bottom waters only show small variations indicative of a consistent influence of Atlantic waters. Since the major intensification of the Northern Hemisphere Glaciation at 2.7 Ma the seawater Nd isotope composition has varied more pronouncedly due to changes in weathering inputs related to the waxing and waning of the ice sheets on Svalbard, the Barents Sea, and the Eurasian shelf, due to changes in water mass exchange and due to the increasing supply of ice-rafted debris (IRD) originating from the Arctic Ocean. The seawater Pb isotope record also exhibits a higher short-term variability after 2.7 Ma, but there is also a trend toward more radiogenic values, which reflects a combination of changes in input sources and enhanced incongruent weathering inputs of Pb released from freshly eroded old continental rocks.

Simulation of the effects of proposed tide gates on circulation, flushing, and water quality in residential canals, Cape Coral Florida

USGS Publications Warehouse

Goodwin, Carl R.

1991-01-01

Decades of dredging and filling of Florida's low-lying coastal wetlands have produced thousands of miles of residential tidal canals and adjacent waterfront property. Typically, these canals are poorly flushed, and over time, accumulated organic-rich bottom materials, contribute to an increasingly severe degraded water quality. One-dimensional hydrodynamic and constituent-transport models were applied to two dead-end canal systems to determine the effects of canal system interconnection using tide gates on water circulation and constituent flushing. The model simulates existing and possible future circulation and flushing conditions in about 29 miles of the approximately 130 miles of tidally influenced canals in Cape Coral, located on the central west coast of peninsular Florida. Model results indicate that tidal water-level differences between the two canal systems can be converted to kinetic energy, in the form of increased water circulation, but the use of one-way tide gate interconnections. Computations show that construction of from one to four tide gates will cause replacement of a volume of water equivalent to the total volume of canals in both systems in 15 to 9 days, respectively. Because some canals flush faster than others, 47 and 21 percent of the original canal water will remain in both systems 50 days after start of operation of one and four tide gates, respectively. Some of the effects that such increased flushing are expected to have include reduced density stratification and associated dissolved-oxygen depletion in canal bottom waters, increased localized reaeration, and more efficient discharge of stormwater runoff entering the canals.

Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in and near Humboldt Wildlife Management Area, Churchill and Pershing Counties, Nevada, 1990-91

USGS Publications Warehouse

Seiler, R.L.; Ekechukwu, G.A.; Hallock, R.J.

1993-01-01

A reconnaissance investigation was begun in 1990 to determine whether the quality of irrigation drainage in and near the Humboldt Wildlife Management Area, Nevada, has caused or has the potential to cause harmful effects on human health, fish, and wildlife or to impair beneficial uses of water. Samples of surface and ground water, bottom sediment, and biota collected from sites upstream and downstream from the Lovelock agricultural area were analyzed for potentially toxic trace elements. Also analyzed were radioactive substances, major dissolved constitu- ents, and nutrients in water, as well as pesticide residues in bottom sediment and biota. In samples from areas affected by irrigation drainage, the following constituents equaled or exceeded baseline concentrations or recommended standards for protection of aquatic life or propagation of wildlife--in water: arsenic, boron, dissolved solids, mercury, molybdenum, selenium, sodium, and un-ionized ammonia; in bottom sediment; arsenic and uranium; and in biota; arsenic, boron, and selenium. Selenium appears to be biomagnified in the Humboldt Sink wetlands. Biological effects observed during the reconnaissance included reduced insect diversity in sites receiving irrigation drainage and acute toxicity of drain water and sediment to test organisms. The current drought and upstream consumption of water for irrigation have reduced water deliveries to the wetlands and caused habitat degradation at Humboldt Wildlife Management Area. During this investigation. Humboldt and Toulon Lakes evaporated to dryness because of the reduced water deliveries.

Rare-earth elements in the Permian Phosphoria Formation: Paleo proxies of ocean geochemistry

USGS Publications Warehouse

Piper, D.Z.; Perkins, R.B.; Rowe, H.D.

2007-01-01

The geochemistry of deposition of the Meade Peak Member of the Phosphoria Formation (MPM) in southeast Idaho, USA, a world-class sedimentary phosphate deposit of Permian age that extends over 300,000 km2, is ascertained from its rare earth element (REE) composition. Ratios of REE:Al2O3 suggest two sources-seawater and terrigenous debris. The seawater-derived marine fraction identifies bottom water in the Phosphoria Sea as O2-depleted, denitrifying (suboxic) most of the time, and seldom sulfate-reducing (anoxic). This interpretation is supported by earlier research that showed progressively greater ratios in the marine sediment fraction of Cr:Ni>V:Ni???Mo:Ni, relative to their ratios in seawater; for which marine Cr, V, and Mo can have a dominantly O2-depleted bottom-water source and Ni a photic-zone, largely algal, source. The water chemistry was maintained by a balance between bacterial oxidation of organic matter settling through the water column, determined largely by primary productivity in the photic zone, and the flux of oxidants into the bottom water via advection of seawater from the open ocean. Samples strongly enriched in carbonate fluorapatite, the dominant REE host mineral, have variable Er/Sm, Tm/Sm, and Yb/Sm ratios. Their distribution may represent greater advection of seawater between the Phosphoria Sea and open ocean during deposition of two ore zones than a center waste and greater upwelling of nutrient-enriched water into the photic zone. However, the mean rate of deposition of marine Ni, a trace nutrient of algae, and PO43-, a limiting nutrient, indicate that primary productivity was probably high throughout the depositional history. An alternative interpretation of the variable enrichments of Er, Tm, and Yb, relative to Sm, is that they may reflect temporally variable carbonate alkalinity of open-ocean seawater in Permian time. A more strongly negative Ce anomaly for all phosphatic units than the Ce anomaly of modern pelletal phosphate is further indicative of an elevated O2 concentration in the Permo-Carboniferous open ocean, as proposed by others, in contrast to the depletion of O2 in the bottom water of the Phosphoria Sea itself. The oceanographic conditions under which the deposit accumulated were likely similar to conditions under which many sedimentary phosphate deposits have accumulated and to conditions under which many black shales that are commonly phosphate poor have accumulated. A shortcoming of several earlier studies of these deposits has resulted from a failure to examine the marine fraction of elements separate from the terrigenous fraction. ?? 2007 Elsevier Ltd. All rights reserved.

Linking benthic hydrodynamics and cold-water coral occurrences: A high-resolution model study at three cold-water coral provinces in the NE Atlantic

NASA Astrophysics Data System (ADS)

Mohn, Christian; Rengstorf, Anna; White, Martin; Duineveld, Gerard; Mienis, Furu; Soetaert, Karline; Grehan, Anthony

2014-03-01

Observations from numerous cold-water coral locations in the NE Atlantic show energetic near-bottom flow dynamics along the European continental margin at individual coral mounds and mound clusters. Dynamics are largely controlled by tide-topography interaction generating and enhancing periodic motions such as trapped waves, freely propagating internal tides and internal hydraulic jumps. In this study, linkages between key abiotic parameters and cold water coral occurrences are explored across entire cold-water coral mound provinces using an integrated modelling and observational approach. The 3-D ocean circulation model ROMS-AGRIF was applied to simulate near-bottom hydrodynamic conditions at three provinces in the NE Atlantic (Logachev mounds, Arc mounds and Belgica mounds) adopting a nested model setup with a central grid resolution of 250 m. Simulations were carried out with a focus on accurate high-resolution topography and tidal forcing. The central model bathymetry was taken from high-resolution INSS (Irish National Seabed Survey) seafloor mapping data. The model was integrated over a full one-year reference period starting from the 1st January 2010. Interannual variability was not considered. Tidal forcing was obtained from a global solution of the Oregon State University (OSU) inverse tidal model. Modelled fields of benthic currents were validated against available independent in situ observations. Coral assemblage patterns (presence and absence locations) were obtained from benthic surveys of the EU FP7 CoralFISH programme and supplemented by data from additional field surveys. Modelled near-bottom currents, temperature and salinity were analysed for a 1-month subset (15th April to 15th May 2010) corresponding to the main CoralFISH survey period. The model results show intensified near-bottom currents in areas where living corals are observed by contrast with coral absence and random background locations. Instantaneous and time-mean current speeds at mound clusters in the Logachev province exceeded typical values in non-coral areas by up to a factor of three. Currents at cold-water coral locations in the Arc and Belgica mound provinces were less energetic, but still elevated compared to non-coral locations. An analysis of dynamical processes associated with oscillatory flow interacting with topography suggests that these motions are locally important food supply mechanisms to cold-water corals by promoting large amplitude local vertical mixing and organic matter fluxes. It is shown that their presence varies considerably between provinces based on the interplay of topographic slope, flow magnitude and ambient stratification.

Rare-earth elements in the Permian Phosphoria Formation: Paleo proxies of ocean geochemistry

NASA Astrophysics Data System (ADS)

Piper, D. Z.; Perkins, R. B.; Rowe, H. D.

2007-06-01

The geochemistry of deposition of the Meade Peak Member of the Phosphoria Formation (MPM) in southeast Idaho, USA, a world-class sedimentary phosphate deposit of Permian age that extends over 300,000 km 2, is ascertained from its rare earth element (REE) composition. Ratios of REE:Al 2O 3 suggest two sources—seawater and terrigenous debris. The seawater-derived marine fraction identifies bottom water in the Phosphoria Sea as O 2-depleted, denitrifying (suboxic) most of the time, and seldom sulfate-reducing (anoxic). This interpretation is supported by earlier research that showed progressively greater ratios in the marine sediment fraction of Cr:Ni>V:Ni≫Mo:Ni, relative to their ratios in seawater; for which marine Cr, V, and Mo can have a dominantly O 2-depleted bottom-water source and Ni a photic-zone, largely algal, source. The water chemistry was maintained by a balance between bacterial oxidation of organic matter settling through the water column, determined largely by primary productivity in the photic zone, and the flux of oxidants into the bottom water via advection of seawater from the open ocean. Samples strongly enriched in carbonate fluorapatite, the dominant REE host mineral, have variable Er/Sm, Tm/Sm, and Yb/Sm ratios. Their distribution may represent greater advection of seawater between the Phosphoria Sea and open ocean during deposition of two ore zones than a center waste and greater upwelling of nutrient-enriched water into the photic zone. However, the mean rate of deposition of marine Ni, a trace nutrient of algae, and PO 43-, a limiting nutrient, indicate that primary productivity was probably high throughout the depositional history. An alternative interpretation of the variable enrichments of Er, Tm, and Yb, relative to Sm, is that they may reflect temporally variable carbonate alkalinity of open-ocean seawater in Permian time. A more strongly negative Ce anomaly for all phosphatic units than the Ce anomaly of modern pelletal phosphate is further indicative of an elevated O 2 concentration in the Permo-Carboniferous open ocean, as proposed by others, in contrast to the depletion of O 2 in the bottom water of the Phosphoria Sea itself. The oceanographic conditions under which the deposit accumulated were likely similar to conditions under which many sedimentary phosphate deposits have accumulated and to conditions under which many black shales that are commonly phosphate poor have accumulated. A shortcoming of several earlier studies of these deposits has resulted from a failure to examine the marine fraction of elements separate from the terrigenous fraction.

Algorithms for Ocean Bottom Albedo Determination from In-Water Natural Light Measurements

NASA Technical Reports Server (NTRS)

Leathers, Robert A.; McCormick, Normal J.

1999-01-01

A method for determining ocean bottom optical albedo, R-sub b, from in-water upward and downward irradiance measurements at a shallow site is presented, tested, and compared with a more familiar approach that requires additional measurements at a nearby deep-water site. Also presented are two new algorithms for the estimation of R-sub b from measurements of the downward irradiance and vertically upward radiance.

Transport of Antarctic Bottom Water through passages in the East Azores Ridge (37° N) in the East Atlantic

NASA Astrophysics Data System (ADS)

Tarakanov, R. Yu.; Morozov, E. G.; Gritsenko, A. M.; Demidova, T. A.; Makarenko, N. I.

2013-07-01

The structure of northerly overflow of Antarctic Bottom Water (AABW) through passages in the East Azores Ridge (37° N) in the East Atlantic from the Madeira Basin to the Iberian Basin is studied on the basis of hydrographic measurements carried out by the Institute of Oceanology, Russian Academy of Sciences (RAS) in October 2011, historical World Ocean Data Base 2009, and recent data on the bottom topography. The overflow of the coldest layers of this water occurs through two passages with close depths at 16° W (Discovery Gap) and at 19°30' W (nameless Western Gap). It is shown that it is likely that the role of the latter passage in water transport was underestimated in earlier publications because the water (2.01°C) found in the region north of the Western Gap was cooler than in the region north of the Discovery Gap (2.03°C). In 2011, we found a decrease of 0.01°C in the AABW temperature near the bottom compared to previous measurements in 1982 (from 2.011°C to 2.002°C). Analysis of the historical database shows that this decrease is most likely caused by the cooling trend in the abyssal waters in the East Atlantic basins.

Pre-fired, refractory block slag dams for wet bottom furnace floors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vihnicka, R.S.; Meskimen, R.L.

1998-12-31

Slagging (wet bottom), utility boilers count on a refractory coating over the furnace floor tube structure for protection from corrosion damage from both the harsh, hot gas atmosphere from the burning fuel and the acidic coal slag. To protect and extend the life of this protective refractory coating the boiler original equipment manufacturers (OEMs) utilized a water-cooled monkey ring or slag chill ring (typically a 6--8 inch high ring of small diameter tubes) surrounding the slag tap locations on most wet bottom furnace floors (both utility and package boilers). The old water-cooled tube ring was such a high maintenance item,more » however, that it`s use has been discontinued in all but the most extreme environments throughout both utility and industrial applications. Where the use of the ring was discontinued, there has been a corresponding shortening of life on the protective floor refractory coatings (high maintenance cost), further aggravated by recent OSHA restrictions limiting the use of chrome oxide refractory materials in these types of boilers. This paper describes the developmental process and the final resultant product (a non-watercooled, slag dam made from pre-fired refractory shapes), undertaken by the inventors. Derived operational benefits a concept 2 project, with NO{sub x} Title 4 and Title 1 significance (which is currently underway) will also be detailed.« less

Geochemistry of the Black Sea during the last 15 kyr: A protracted evolution of its hydrography and ecology

USGS Publications Warehouse

Piper, David Z.

2016-01-01

The Black Sea is a 2200 m deep anoxic, marine sea connected to the Mediterranean Sea via the Dardanelles Strait, Marmara Sea, and the 3 km wide, 35 m deep Bosphorus Strait. The biogeochemistry of sediment from the Anatolia slope has recorded changes to the hydrography leading up to and following the input of Mediterranean water at ~9.4 ka (103 years B.P.), when global sea level rose to the level of the Bosphorus sill and high-salinity water from the Mediterranean began to spill into the then brackish lake. The water initially mixed little with the lake water but cascaded to the bottom where it remained essentially isolated for ~1.6 kyr, the time required to fill the basin from the bottom up at its present input rate. The accumulation of Mo in the seafloor sediments, a proxy of bottom-water anoxia, increased sharply at ~8.6 ka, when bacterial respiration in the bottom water advanced to SO42− reduction by the oxidation of organic detritus that settled out of the photic zone. Its accumulation remained elevated to ~5.6 ka, when it decreased 60%, only to again increase slightly at ~2.0 ka. The accumulation of Corg, a proxy of primary productivity, increased threefold to fourfold at ~7.8 ka, when upward mixing of the high-salinity bottom water replaced the then thin veneer of the brackish photic zone in less than 50 years. From that time onward, the accumulation of Corg, Mo, and additional trace metals has reflected the hydrography of the basin and Bosphorus Strait, controlled largely by climate.

Influence of the hydrodynamic conditions on the accessibility of Aristeus antennatus and other demersal species to the deep water trawl fishery off the Balearic Islands (western Mediterranean)

NASA Astrophysics Data System (ADS)

Amores, Angel; Rueda, Lucía; Monserrat, Sebastià; Guijarro, Beatriz; Pasqual, Catalina; Massutí, Enric

2014-10-01

Monthly catches per unit of effort (CPUE) of adult red shrimp (Aristeus antennatus), reported in the deep water bottom trawl fishery developed on the Sóller fishing ground off northern Mallorca (Western Mediterranean), and the mean ocean surface vorticity in the surrounding areas are compared between 2000 and 2010. A good correlation is found between the rises in the surrounding surface vorticity and the drops in the CPUE of the adult red shrimp. This correlation could be explained by assuming that most of the surface vorticity episodes could reach the bottom, increasing the seabed velocities and producing sediment resuspension, which could affect the near bottom water turbidity. A. antennatus would respond to this increased turbidity disappearing from the fishing grounds, probably moving downwards to the deeper waters. This massive displacement of red shrimp specimens away from the fishing grounds would consequently decrease their accessibility to fishing exploitation. Similar although more intense responses have been observed during the downslope shelf dense water current episodes that occurred in a submarine canyon, northeast of the Iberian peninsula. The proposed mechanism suggesting how the surface vorticity observed can affect the bottom sediments is investigated using a year-long moored near-bottom current meter and a sediment trap moored near the fishing grounds. The relationship between vorticity and catches is also explored for fish species (Galeus melastomus, Micromesistius poutassou, Phycis blennoides) and other crustacean (Geryon longipes and Nephrops norvegicus), considered as by-catch of the deep water fishery in the area. Results appear to support the suggestion that the water turbidity generated by the vorticity episodes is significant enough to affect the dynamics of the demersal species.

General equations for the motions of ice crystals and water drops in gravitational and electric fields

NASA Technical Reports Server (NTRS)

Nisbet, John S.

1988-01-01

General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.

The role of Argopecten purpuratus shells structuring the soft bottom community in shallow waters of southern Peru

NASA Astrophysics Data System (ADS)

Lomovasky, Betina J.; Gamero, Patricia A.; Romero, Leonardo; Firstater, Fausto N.; Gamarra Salazar, Alex; Hidalgo, Fernando; Tarazona, Juan; Iribarne, Oscar O.

2015-12-01

Accumulation of Argopecten purpuratus shells often occurs after El Niño events in shallow waters of Independencia Bay (14°17‧S-76°10‧W; Pisco, Peru). Here we experimentally investigate the effects of their shell accumulation on macrobenthos assemblages in soft bottom, shallow areas of the bay. A field experiment (from May 2006 to May 2007), including four treatments with different coverage levels of empty shells of A. purpuratus, were randomly arranged in: (1) areas devoid of shells ("Empty" treatment: experimental control), (2) 50% of the plot area covered with shells haphazardly distributed over the bottom ("medium" treatment), (3) 100% of the plot area covered with shells, forming a 10 cm valve layer ("full" treatment) and (4) "natural control". We found a total of 124 taxa throughout the experiment. Polychaetes, crustaceans and mollusks were the most abundant groups in "natural controls", dominated by the gastropod Nassarius gayi and the polychaetes Prionospio peruana, Platynereis bicanaliculata and Mediomastus branchiferus. The abundance of individuals (N) and the species richness (S) were higher in the "medium" treatment, but only in one month under positive sea bottom thermal anomalies. Similarity analysis (Bray-Curtis) showed that "natural control", "empty" and "full" treatments were more similar among them than the "medium" treatment. Multidimensional analysis showed no clear species association among treatments and a higher grouping among the samplings of Jun-06, Aug-06 and Nov-06. Our results also showed that the commercial crab Romaleon polyodon and the polyplacophora Tonicia elegans were positively affected by shell accumulations ("medium" treatment), while the limpet Fissurella crassa was negatively affected. Our study shows that directly by changing habitat structure or indirectly by changing sediment characteristics, the addition of scallop shells to the soft bottom can modify the macrobenthic assemblage; however, the seasonal oceanographic variability (e.g. upwelling, El Niño) could have stronger effects controlling this system than the presence of the shells itself.

Wave and setup dynamics on steeply-sloping reefs with large bottom roughness

NASA Astrophysics Data System (ADS)

Buckley, M. L.; Hansen, J.; Lowe, R.

2016-12-01

High-resolution observations from a wave flume were used to investigate the dynamics of wave setup over a steeply-sloping fringing reef profile with the effect of bottom roughness modeled using roughness elements scaled to mimic a coral reef. Results with roughness were compared with smooth bottom runs across sixteen offshore wave and still water level conditions. The time-averaged and depth-integrated force balance was evaluated from observations collected at seventeen locations across the flume, which was found to consist of cross-shore pressure and radiation stress gradients whose sum was balanced by mean quadratic bottom stresses. We found that when radiation stress gradients were calculated from observations of the radiation stress derived from linear wave theory, both wave setdown and setup were under predicted for the majority of wave and water level conditions tested. Inaccuracies in the predicted setdown and setup were improved by including a wave roller model, which provides a correction to the kinetic energy predicted by linear wave theory for breaking waves and produces a spatial delay in the wave forcing that was consistent with the observations. The introduction of roughness had two primary effects. First, the amount of wave energy dissipated during wave breaking was reduced due to frictional wave dissipation that occurred on the reef slope offshore of the breakpoint. Second, offshore directed mean bottom stresses were generated by the interaction of the combined wave-current velocity field with the roughness elements. These two mechanisms acted counter to one another. As a result, setup on the reef flat was comparable (7% mean difference) between corresponding rough and smooth runs. These findings are used to assess prior results from numerical modelling studies of reefs, and also to discuss the broader implications for how steep slopes and large roughness influences setup dynamics for general nearshore systems.

Quantifying hyporheic exchange in a karst stream using 222Rn

NASA Astrophysics Data System (ADS)

Khadka, M. B.; Martin, J. B.; Kurz, M. J.

2013-12-01

The hyporheic zone is a critical interface between groundwater and river water environments and is characterized by steep biogeochemical gradients. Understanding how this interface affects solute transport, nutrient cycling and contaminant attenuation is essential for better water resource management of streams. However, this understanding is constrained due to difficulty associated with quantification of exchange of water through the hyporheic zone. We tested a radon (222Rn) method to estimate the hyporheic water residence time and exchange rate in the bottom sediment of the spring-fed Ichetucknee River, north-central Florida. The river, which flows over the top of the unconfined karstic Floridan Aquifer, is characterized by a broad bedrock channel partially in-filled with unconsolidated sediments. Radon (222Rn) activity in the pore waters of the channel sediments differs from the amount expected from sediment production and decay. Although most radon in streams originates from sources in bottom sediments, the Ichetucknee River water has 222Rn activities (251×5 PCi/L) that are nearly twice that of the pore water (128×15 PCi/L). The river water 222Rn activity is consistent with that of the source springs, suggesting the source of Rn in the river is from deep within the aquifer rather than bottom sediments and that the excess 222Rn in the pore water results from hyporheic exchange. Profiles of radon concentrations with depth through the sediments show that the mixing of stream water and pore water extends 35-45 cm below the sediment and water interface. Based on a model that integrates the excess radon with depth, we estimate the water exchange rate to be between 1.1 and 1.6 cm/day with an average value of 1.3×0.2 cm/day. Water that exchanges across the sediment-water interface pumps oxygen into the sediments, thereby enhancing organic carbon remineralization, as well as the production of NH4+ and PO43- and their fluxes from sediments to the stream. As opposed to conventional in-stream tracer injection method which estimates exchange between the stream and both the hyporheic zone and the surface transient storage zone, the 222Rn approach measures the water exchange between stream and hyporheic sediments only. Although the present method is tested on a spring-fed karst stream, it has potential for any freshwater system (e.g. wetland, lake) where distinct radon activity and production between surface water and underlying sediments occur.

Water color and circulation southern Chesapeake Bay, part 1

NASA Technical Reports Server (NTRS)

Nichols, M. M.; Gordon, H. H.

1975-01-01

Satellite imagery from two EREP passes over the Rappahannock Estuary of the Chesapeake region is analyzed to chart colored water types, to delineate color boundaries and define circulatory patterns. Surface observations from boats and helicopters concurrent with Skylab overpass define the distributions of suspended sediment, transparency, temperature, salinity, phytoplankton, color of suspended material and optical ratio. Important features recorded by the imagery are a large-scale turbidity maximum and massive red tide blooms. Water movement is revealed by small-scale mixing patterns and tidal plumes of apparent sediment-laden water. The color patterns broadly reflect the bottom topography and the seaward gradient of suspended material between the river and the bay. Analyses of red, green and natural color photos by microdensitometry demonstrate the utility of charting water color types of potential use for managing estuarine water quality. The Skylab imagery is superior to aerial photography and surface observations for charting water color.

A NON-STEADY-STATE DIAGENETIC MODEL FOR CHANGES IN SEDIMENT BIOGEOCHEMISTRY IN RESPONSE TO SEASONALLY HYPOXIC/ANOXIC CONDITIONS BENEATH THE MISSISSIPPI RIVER PLUME

EPA Science Inventory

Although the bottom waters of many freshwater and marine environments are either permanently oxic or anoxic, there is a growing appreciation that in many bodies of water near-bottom conditions seasonally oscillate between these extreme. Although observational databases for these ...

Investigating the importance of sediment resuspension in Alexandrium fundyense cyst population dynamics in the Gulf of Maine

USGS Publications Warehouse

Butman, Bradford; Aretxabaleta, Alfredo L.; Dickhudt, Patrick J.; Dalyander, P. Soupy; Sherwood, Christopher R.; Anderson, Donald M.; Keafer, Bruce A.; Signell, Richard P.

2014-01-01

Cysts of Alexandrium fundyense, a dinoflagellate that causes toxic algal blooms in the Gulf of Maine, spend the winter as dormant cells in the upper layer of bottom sediment or the bottom nepheloid layer and germinate in spring to initiate new blooms. Erosion measurements were made on sediment cores collected at seven stations in the Gulf of Maine in the autumn of 2011 to explore if resuspension (by waves and currents) could change the distribution of over-wintering cysts from patterns observed in the previous autumn; or if resuspension could contribute cysts to the water column during spring when cysts are viable. The mass of sediment eroded from the core surface at 0.4 Pa ranged from 0.05 kg m−2 near Grand Manan Island, to 0.35 kg m−2 in northern Wilkinson Basin. The depth of sediment eroded ranged from about 0.05 mm at a station with sandy sediment at 70 m water depth on the western Maine shelf, to about 1.2 mm in clayey–silt sediment at 250 m water depth in northern Wilkinson Basin. The sediment erodibility measurements were used in a sediment-transport model forced with modeled waves and currents for the period October 1, 2010 to May 31, 2011 to predict resuspension and bed erosion. The simulated spatial distribution and variation of bottom shear stress was controlled by the strength of the semi-diurnal tidal currents, which decrease from east to west along the Maine coast, and oscillatory wave-induced currents, which are strongest in shallow water. Simulations showed occasional sediment resuspension along the central and western Maine coast associated with storms, steady resuspension on the eastern Maine shelf and in the Bay of Fundy associated with tidal currents, no resuspension in northern Wilkinson Basin, and very small resuspension in western Jordan Basin. The sediment response in the model depended primarily on the profile of sediment erodibility, strength and time history of bottom stress, consolidation time scale, and the current in the water column. Based on analysis of wave data from offshore buoys from 1996 to 2012, the number of wave events inducing a bottom shear stress large enough to resuspend sediment at 80 m ranged from 0 to 2 in spring (April and May) and 0 to 10 in winter (October through March). Wave-induced resuspension is unlikely in water greater than about 100 m deep. The observations and model results suggest that a millimeter or so of sediment and associated cysts may be mobilized in both winter and spring, and that the frequency of resuspension will vary interannually. Depending on cyst concentration in the sediment and the vertical distribution in the water column, these events could result in a concentration in the water column of at least 104 cysts m−3. In some years, resuspension events could episodically introduce cysts into the water column in spring, where germination is likely to be facilitated at the time of bloom formation. An assessment of the quantitative effects of cyst resuspension on bloom dynamics in any particular year requires more detailed investigation.

Hydrology and trout populations of cold-water rivers of Michigan and Wisconsin

USGS Publications Warehouse

Hendrickson, G.E.; Knutilla, R.L.

1974-01-01

Statistical multiple-regression analyses showed significant relationships between trout populations and hydrologic parameters. Parameters showing the higher levels of significance were temperature, hardness of water, percentage of gravel bottom, percentage of bottom vegetation, variability of streamflow, and discharge per unit drainage area. Trout populations increase with lower levels of annual maximum water temperatures, with increase in water hardness, and with increase in percentage of gravel and bottom vegetation. Trout populations also increase with decrease in variability of streamflow, and with increase in discharge per unit drainage area. Most hydrologic parameters were significant when evaluated collectively, but no parameter, by itself, showed a high degree of correlation with trout populations in regression analyses that included all the streams sampled. Regression analyses of stream segments that were restricted to certain limits of hardness, temperature, or percentage of gravel bottom showed improvements in correlation. Analyses of trout populations, in pounds per acre and pounds per mile and hydrologic parameters resulted in regression equations from which trout populations could be estimated with standard errors of 89 and 84 per cent, respectively.

Modification of deep waters in Marguerite Bay, western Antarctic Peninsula, caused by topographic overflows

NASA Astrophysics Data System (ADS)

Venables, Hugh J.; Meredith, Michael P.; Brearley, J. Alexander

2017-05-01

Circumpolar Deep Water (CDW) intrudes from the mid-layers of the Antarctic Circumpolar Current onto the shelf of the western Antarctic Peninsula, providing a source of heat and nutrients to the regional ocean. It is well known that CDW is modified as it flows across the shelf, but the mechanisms responsible for this are not fully known. Here, data from underwater gliders with high spatial resolution are used to demonstrate the importance of detailed bathymetry in inducing multiple local mixing events. Clear evidence for overflows is observed in the glider data as water flows along a deep channel with multiple transverse ridges. The ridges block the densest waters, with overflowing water descending several hundred metres to fill subsequent basins. This vertical flow leads to entrainment of overlying colder and fresher water in localised mixing events. Initially this process leads to an increase in bottom temperatures due to the temperature maximum waters descending to greater depths. After several ridges, however, the mixing is sufficient to remove the temperature maximum completely and the entrainment of colder thermocline waters to depth reduces the bottom temperature, to approximately the same as in the source region of Marguerite Trough. Similarly, it is shown that deep waters of Palmer Deep are warmer than at the same depth at the shelf break. The exact details of the transformations observed are heavily dependent on the local bathymetry and water column structure, but glacially-carved troughs and shallow sills are a common feature of the bathymetry of polar shelves, and these types of processes may be a factor in determining the hydrographic conditions close to the coast across a wider area.

Plunge location of sediment driven hyperpycnal river discharges considering bottom friction, lateral entrainment, and particle settling

NASA Astrophysics Data System (ADS)

Strom, K. B.; Bhattacharya, J.

2012-12-01

River discharges with very high sediment loads have the potential to develop into plunging hyperpycnal flows that transition from a river jet to a turbidity current at some location basinward of the river mouth due to the density difference between the turbid river and the receiving water body. However, even if the bulk density of the turbid river is greater than that of the receiving lake or ocean, some distance is needed for the forward inertia of the river to dissipate so that the downward gravitational pull can cause the system to collapse into a subaqueous turbidity current. This collapsing at the plunge point has been found to occur when the densimetric Froude number decreases to a value between 0.3 < Frd < 0.7 (Fang and Stefan 2000, Parker and Toniolo 2007, Dai and Garcia 2010, Lamb et al. 2010). In 2D channel flow analysis at the plunge point, this has led to the concept of a two-fold criterion for plunging. The first is simply for the need of high enough suspended sediment concentration to overcome the density difference between the river fluid and the fluid of the receiving water. The second is the need for sufficiently deep water to reduce the densimetric Froude below the critical value for plunging, which leads to dependence of plunging on the receiving water basin topography (Lamb et al. 2010). In this analysis, we expand on past work by solving a system of ODE river jet equations to account for bottom friction, lateral entrainment of ambient fluid, and particle settling between the river mouth and the plunge location. Typical entrainment and bottom friction coefficients are used and the model is tested against the laboratory density current data of Fang and Stefan (1991). A suite of conditions is solved with variable river discharge velocity, aspect ratio, suspended sediment concentration, and particle size; a range of salinity values and bottom slopes are used for the receiving water body. The plunge location is then expressed as a function of the boundary conditions at the river mouth and those of the receiving water. The relationships can be used for modern systems, but can also help to put reasonable bounds on paleo-hydraulic setting. References Dai, A. & Garcia, M. H. (2010). Energy Dissipative Plunging Flows. Journal of Hydraulic Engineering, 136(8), 519-523. Fang, X. & Stefan, H. G. (1991). Integral Jet Model for Flow from an Open Channel into a Shallow Lake or Reservoir. St. Anthony Falls Hydraulic Laboratory. Fang, X. & Stefan, H. G. (2000). Dependence of dilution of a plunging discharge over a sloping bottom on inflow conditions and bottom friction. Journal of Hydraulic Research, 38(1), 15-25. Lamb, M. P., McElroy, B., Kopriva, B., Shaw, J., & Mohrig, D. (2010). Linking river-flood dynamics to hyperpycnal-plume deposits: Experiments, theory, and geological implications. Geological Society of America Bulletin, 122(9/10), 1389-1400. Parker, G. & Toniolo, H. (2007). Note on the Analysis of Plunging of Density Flows. Journal of Hydraulic Engineering, 133(6), 690-694.

Abyssal Upwelling and Downwelling and the role of boundary layers

NASA Astrophysics Data System (ADS)

McDougall, T. J.; Ferrari, R. M.

2016-02-01

The bottom-intensified mixing activity arising from the interaction of internal tides with bottom topography implies that the dianeutral advection in the ocean interior is downwards, rather than upwards as is required by continuity. The upwelling of Bottom Water through density surfaces in the deep ocean is however possible because of the sloping nature of the sea floor. A budget study of the abyss (deeper than 2000m) will be described that shows that while the upwelling of Bottom Water might be 25 Sv, this is achieved by very strong upwelling in the bottom turbulent boundary layer (of thickness 50m) of 100 Sv and strong downwelling in the ocean interior of 75 Sv. This downwelling occurs within 10 degrees of longitude of the continental boundaries. This near-boundary confined strong upwelling and downwelling clearly has implications for the Stommel-Arons circulation.

A coupled-mode model for the hydroelastic analysis of large floating bodies over variable bathymetry regions

NASA Astrophysics Data System (ADS)

Belibassakis, K. A.; Athanassoulis, G. A.

2005-05-01

The consistent coupled-mode theory (Athanassoulis & Belibassakis, J. Fluid Mech. vol. 389, 1999, p. 275) is extended and applied to the hydroelastic analysis of large floating bodies of shallow draught or ice sheets of small and uniform thickness, lying over variable bathymetry regions. A parallel-contour bathymetry is assumed, characterized by a continuous depth function of the form h( {x,y}) {=} h( x ), attaining constant, but possibly different, values in the semi-infinite regions x {<} a and x {>} b. We consider the scattering problem of harmonic, obliquely incident, surface waves, under the combined effects of variable bathymetry and a floating elastic plate, extending from x {=} a to x {=} b and {-} infty {<} y{<}infty . Under the assumption of small-amplitude incident waves and small plate deflections, the hydroelastic problem is formulated within the context of linearized water-wave and thin-elastic-plate theory. The problem is reformulated as a transition problem in a bounded domain, for which an equivalent, Luke-type (unconstrained), variational principle is given. In order to consistently treat the wave field beneath the elastic floating plate, down to the sloping bottom boundary, a complete, local, hydroelastic-mode series expansion of the wave field is used, enhanced by an appropriate sloping-bottom mode. The latter enables the consistent satisfaction of the Neumann bottom-boundary condition on a general topography. By introducing this expansion into the variational principle, an equivalent coupled-mode system of horizontal equations in the plate region (a {≤} x {≤} b) is derived. Boundary conditions are also provided by the variational principle, ensuring the complete matching of the wave field at the vertical interfaces (x{=}a and x{=}b), and the requirements that the edges of the plate are free of moment and shear force. Numerical results concerning floating structures lying over flat, shoaling and corrugated seabeds are presented and compared, and the effects of wave direction, bottom slope and bottom corrugations on the hydroelastic response are presented and discussed. The present method can be easily extended to the fully three-dimensional hydroelastic problem, including bodies or structures characterized by variable thickness (draught), flexural rigidity and mass distributions.

Innovative open air brayton combined cycle systems for the next generation nuclear power plants

NASA Astrophysics Data System (ADS)

Zohuri, Bahman

The purpose of this research was to model and analyze a nuclear heated multi-turbine power conversion system operating with atmospheric air as the working fluid. The air is heated by a molten salt, or liquid metal, to gas heat exchanger reaching a peak temperature of 660 0C. The effects of adding a recuperator or a bottoming steam cycle have been addressed. The calculated results are intended to identify paths for future work on the next generation nuclear power plant (GEN-IV). This document describes the proposed system in sufficient detail to communicate a good understanding of the overall system, its components, and intended uses. The architecture is described at the conceptual level, and does not replace a detailed design document. The main part of the study focused on a Brayton --- Rankine Combined Cycle system and a Recuperated Brayton Cycle since they offer the highest overall efficiencies. Open Air Brayton power cycles also require low cooling water flows relative to other power cycles. Although the Recuperated Brayton Cycle achieves an overall efficiency slightly less that the Brayton --- Rankine Combined Cycle, it is completely free of a circulating water system and can be used in a desert climate. Detailed results of modeling a combined cycle Brayton-Rankine power conversion system are presented. The Rankine bottoming cycle appears to offer a slight efficiency advantage over the recuperated Brayton cycle. Both offer very significant advantages over current generation Light Water Reactor steam cycles. The combined cycle was optimized as a unit and lower pressure Rankine systems seem to be more efficient. The combined cycle requires a lot less circulating water than current power plants. The open-air Brayton systems appear to be worth investigating, if the higher temperatures predicted for the Next Generation Nuclear Plant do materialize.

Assessing Resiliency in a Large Lake Receiving Mine Tailings Waste: Impacts of Major Environmental Disturbance.

NASA Astrophysics Data System (ADS)

Petticrew, Ellen; Owens, Philip; Albers, Sam

2016-04-01

On 4th August 2014, the tailings impoundment of the Mount Polley copper and gold mine in British Columbia failed. Material from the impoundment (surface area = 2.7 km2) flowed into nearby Polley Lake and Hazeltine Creek, before discharging into Quesnel Lake, a large (ca. 100 km long, >500 m deep), relatively pristine lake. Initial estimates suggest that approximately 25 Mm3 of tailings (water and solids) and eroded soils and surficial materials from Hazeltine Creek were delivered to Quesnel Lake, raising the lake by 7.7 cm. Much of this material was deposited at the bottom of Quesnel Lake but a plume of fine-grained sediment (D50 of ca. 1 μm) remained suspended in the water column. The impact of the distribution of this sediment was monitored over the next 15 months using water column profiling for temperature, conductivity, fluorescence and turbidity with depth. The plume movement was regulated by natural processes associated with the physical limnology of this large fjord lake, specifically, seiche events which transferred suspended particles both up-lake, against the flow regime, and down-lake into the Quesnel River. Samples of lake water and bottom sediment taken from the impacted area show elevated levels of total metals and other elements, which may have important ecosystem implications in this watershed. Indeed, the breach occurred at a time when a peak run of sockeye salmon were returning to their natal streams in the Quesnel basin. Zooplankton sampling for metals was initiated in fall 2014 to determine up take of metals into the food web. This poster describes the failure of the impoundment dam and presents results of sampling the aquatic environment over the first fifteen months of impact.

The helium isotopic chemistry of Lake Bonney, Taylor Valley, Antarctica: Timing of late holocene climate change in Antarctica

USGS Publications Warehouse

Poreda, R.J.; Hunt, A.G.; Berry, Lyons W.; Welch, K.A.

2004-01-01

To better understand the long-term climate history of Antarctica, we studied Lake Bonney in Taylor Valley, Southern Victoria Land (78?? S). Helium isotope ratios and He, Ne, Ar and N2 concentration data, obtained from hydrocasts in the East (ELB) and West (WLB) Lobesof Lake Bonney, provided important constraints on the lake's Holocene evolution. Based on very low concentrations of Ar and N2 in the ELB bottom waters, ELB was free of ice until 200 ?? 50 years ago. After which, low salinity water flowing over the sill from WLB to ELB, covered ELB and formed a perennial ice cover, inhibiting the exchange of gases with the atmosphere. In contrast to the ELB, the WLB retained an ice cover through the Holocene. The brine in the WLB bottom waters has meteoric N2 and Ar gas concentrations indicating that it has not been significantly modified by atmospheric exchange or ice formation. The helium concentrations in the deep water of WLB are the highest measured in non-thermal surface water. By fitting a diffusional loss to the 3He/4He, helium, and Cl profiles, we calculate a time of ???3000 years for the initiation of flow over the sill separating the East and West Lobes. To supply this flux of helium to the lake, a helium-rich sediment beneath the lake must be providing the helium by diffusion. If at any time during the last million years the ice cover left WLB, there would be insufficient helium available to provide the current flux to WLB. The variations in water levels in Lake Bonney can be related to climatic events that have been documented within the Southern Victoria Land region and indicate that the lakes respond significantly to regional and, perhaps, global climate forcing. ?? 2004 Kluwer Academic Publishers.

Contamination of estuarine water, biota, and sediment by halogenated organic compounds: A field study

USGS Publications Warehouse

Pereira, W.E.; Rostad, C.E.; Chiou, C.T.; Brinton, T.I.; Barber, L.B.; Demcheck, D.K.; Demas, C.R.

1988-01-01

Studies conducted in the vicinity of an industrial outfall in the Calcasieu River estuary, Louisiana, have shown that water, bottom and suspended sediment, and four different species of biota are contaminated with halogenated organic compounds (HOC) including haloarenes. A "salting-out" effect in the estuary moderately enhanced the partitioning tendency of the contaminants into biota and sediments. Contaminant concentrations in water, suspended sediments, and biota were found to be far below the values predicted on the basis of the assumption of phase equilibria with respect to concentrations in bottom sediment. Relative concentration factors of HOC between biota (catfish) and bottom sediment increased with increasing octanol/estuarine water partition coefficients (Kow*), maximizing at log Kow* of about 5, although these ratios were considerably less than equilibrium values. In contrast, contaminant concentrations in water, biota, and suspended sediments were much closer to equilibrium values. Bioconcentration factors of HOC determined on the basis of lipid content for four different biotic species correlated reasonably well with equilibrium triolein/water partition coefficients (Ktw).

Near-inertial motions over a mid-Ocean Ridge; Effects of topography and hydrothermal plumes

NASA Astrophysics Data System (ADS)

Thomson, Richard E.; Roth, Sharon E.; Dymond, Jack

1990-05-01

We investigate the spatial structure of near-inertial motions in the vicinity of the Endeavour segment of Juan de Fuca Ridge (approximately 48°N, 129°W) in the northeast Pacific Ocean. On the basis of time series current and water property data collected from September 1984 to September 1987, near-inertial motions are ubiquitous features of the 2200-m water column, with root-mean-square (rms) current speeds comparable to those of the dominant M2 tidal currents. Within the lower 1000 m of the water column where most of the observations were obtained, near-inertial oscillations have rms current speeds of O(1 cm/s) and vertical isotherm displacements of O(10 m). The fluctuations are confined to the frequency band 0.966-1.079 f(f is the local Coriolis parameter) and have characteristic event durations of 1 week. Although the spectra of subsurface motions are dominated by the "blue-shifted" superinertial band, significant spectral peaks are found also in the subinertial and inertial frequency bands. Marked alteration of the near-inertial current amplitudes occurs over two well-defined depth zones within the study region. Within the 200-m zone immediately above the 2100-m ridge crest, current amplitudes are amplified by a factor of 1.2-1.7 because of bottom reflection and/or scattering of the downward propagating energy. Evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross-slope rotation of the near-inertial current ellipses with increased proximity to the top of the ridge. Reflection would occur at grazing angles of less than 1° and would be associated with surface-generated waves originating at distances of over 100 km from the observational site. In contrast to the enhanced amplitudes immediately above the top of the ridge, near-inertial currents within the 1600- to 1800-m depth range undergo pronounced attenuation and frequency alteration. Amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical-layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow. The increased shear is most likely associated with buoyancy-induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest, but it could also be related to bottom-trapped oscillations over the steep ridge topography. Near-inertial motions are estimated to have vertical coherence scales of the order of 10-100 m, while horizontal coherence scales exceed the 50-km separation between the mooring locations. Minimum vertical and horizontal coherences are found for the depth zone 1600-1800 m, while maximum correlation occurs for near-bottom motions immediately above the crest of the ridge. Weak near-inertial motions are observed within the 100-m-deep axial valley.

Quantitative estimation of surface ocean productivity and bottom water oxygen concentration using benthic foraminifera

NASA Astrophysics Data System (ADS)

Loubere, Paul

1994-10-01

An electronic supplement of this material may be obtained on adiskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN toAGU's FTP account using ANONYMOUS as the usemame andGUEST as the password. Go to the right directory by typing CDAPEND. Type LS to see what files are available. Type GET and thename of the file to get it. Finally, type EXIT to leave the system.)(Paper 94PA01624, Quantitative estimation of surface oceanproductivity and bottom water concentration using benthicforaminifera, by P. Loubere). Diskette may be ordered from AmericanGeophysical Union, 2000 Florida Avenue, N.W., Washington, DC20009; $15.00. Payment must accompany order.Quantitative estimation of surface ocean productivity and bottom water oxygen concentration with benthic foraminifera was attempted using 70 samples from equatorial and North Pacific surface sediments. These samples come from a well defined depth range in the ocean, between 2200 and 3200 m, so that depth related factors do not interfere with the estimation. Samples were selected so that foraminifera were well preserved in the sediments and temperature and salinity were nearly uniform (T = 1.5° C; S = 34.6‰). The sample set was also assembled so as to minimize the correlation often seen between surface ocean productivity and bottom water oxygen values (r² = 0.23 for prediction purposes in this case). This procedure reduced the chances of spurious results due to correlations between the environmental variables. The samples encompass a range of productivities from about 25 to >300 gC m-2 yr-1, and a bottom water oxygen range from 1.8 to 3.5 ml/L. Benthic foraminiferal assemblages were quantified using the >62 µm fraction of the sediments and 46 taxon categories. MANOVA multivariate regression was used to project the faunal matrix onto the two environmental dimensions using published values for productivity and bottom water oxygen to calibrate this operation. The success of this regression was measured with the multivariate r² which was 0.98 for the productivity dimension and 0.96 for the oxygen dimension. These high coefficients indicate that both environmental variables are strongly imbedded in the faunal data matrix. Analysis of the beta regression coefficients shows that the environmental signals are carried by groups of taxa which are consistent with previous work characterizing benthic foraminiferal responses to productivity and bottom water oxygen. The results of this study suggest that benthic foraminiferal assemblages can be used for quantitative reconstruction of surface ocean productivity and bottom water oxygen concentrations if suitable surface sediment calibration data sets are developed and appropriate means for detecting no-analog samples are found.

Final Scientific/Technical Report: Characterizing the Response of the Cascadia Margin Gas Hydrate Reservoir to Bottom Water Warming Along the Upper Continental Slope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solomon, Evan A.; Johnson, H. Paul; Salmi, Marie

The objective of this project is to understand the response of the WA margin gas hydrate system to contemporary warming of bottom water along the upper continental slope. Through pre-cruise analysis and modeling of archive and recent geophysical and oceanographic data, we (1) inventoried bottom simulating reflectors along the WA margin and defined the upper limit of gas hydrate stability, (2) refined margin-wide estimates of heat flow and geothermal gradients, (3) characterized decadal scale temporal variations of bottom water temperatures at the upper continental slope of the Washington margin, and (4) used numerical simulations to provide quantitative estimates of howmore » the shallow boundary of methane hydrate stability responds to modern environmental change. These pre-cruise results provided the context for a systematic geophysical and geochemical survey of methane seepage along the upper continental slope from 48° to 46°N during a 10-day field program on the R/V Thompson from October 10-19, 2014. This systematic inventory of methane emissions along this climate-sensitive margin corridor and comprehensive sediment and water column sampling program provided data and samples for Phase 3 of this project that focused on determining fluid and methane sources (deep-source vs. shallow; microbial, thermogenic, gas hydrate dissociation) within the sediment, and how they relate to contemporary intermediate water warming. During the 2014 research expedition, we sampled nine seep sites between ~470 and 520 m water depth, within the zone of predicted methane hydrate retreat over the past 40 years. We imaged 22 bubble plumes with heights commonly rising to ~300 meters below sea level with one reaching near the sea surface. We collected 22 gravity cores and 20 CTD/hydrocasts from the 9 seeps and at background locations (no acoustic evidence of seepage) within the depth interval of predicted downslope retreat of the methane hydrate stability zone. Approximately 300 pore water samples were extracted from the gravity cores, and the pore water was analyzed for a comprehensive suite of solutes, gases, and stable isotope ratios. This comprehensive geochemical dataset was used to characterize the fluid and gas source(s) at each of the seep sites surveyed. The primary results of this project are: 1) Bottom simulating reflector-derived heat flow values decrease from 95 mW/m2 10 km east of the deformation front to ~60 mW/m2 60 km landward of the deformation front, with anomalously low values of ~25 mW/m2 on a prominent mid-margin terrace off central Washington. 2) The temperature of the incoming sediment/ocean crust interface at the deformation front ranges between 164-179 oC off central Washington, and the 350 oC isotherm at the top of the subducting ocean crust occurs 95 km landward of the deformation front. Differences between BSR-derived heat flow and modeled conductive heat flow suggest mean upward fluid flow rates of 0.4 cm/yr across the margin, with local regions (e.g. fault zones) exhibiting fluid flow rates up to 3.5 cm/yr. 3) A compilation of 2122 high-resolution CTD, glider, and Argo float temperature profiles spanning the upper continental slope of the Washington margin from the years 1968 to 2013 show a long-term warming trend that ranges from 0.006-0.008 oC/yr. Based on this long-term bottom water warming, we developed a 2-D thermal model to simulate the change in sediment temperature distribution over this period, along with the downslope retreat of the methane hydrate stability field. Over the 43 years of the simulation, the thermal disturbance propagated 30 m into the sediment column, causing the base of the methane hydrate stability field to shoal ~13 m and to move ~1 km downslope. 4) A preliminary analysis of seafloor observations and mid-water column acoustic data to detect bubble plumes was used to characterize the depth distribution of seeps along the Cascadia margin. These results indicate high bubble plume densities along the continental shelf at water depths <180 m and at the upper limit of methane hydrate stability along the Washington margin. 5) The majority of the seeps cored during the 2014 research expedition on the R/V Thompson contained abundant authigenic carbonate indicating that they are locations of long-lived seepage rather than emergent seep systems related to methane hydrate dissociation. Despite the evidence for enhanced methane seepage at the upper limit of methane hydrate stability along the Washington margin, we found no unequivocal evidence for active methane hydrate dissociation as a source of fluid and gas at the seeps surveyed. The pore fluid and bottom water chemistry shows that the seeps are fed by a variety of fluid and methane sources, but that methane hydrate dissociation, if occurring, is not widespread and is only a minor source (below the detection limit of our methods). Collectively, these results provide a significant advance in our understanding of the thermal structure of the Cascadia subduction zone and the fluid and methane sources feeding seeps along the upper continental slope of the Washington-sector of the Cascadia margin. Though we did not find unequivocal evidence for methane hydrate dissociation as a source of water and methane at the upper pressure-temperature limit of methane hydrate stability at present, continued warming of North Pacific Intermediate Water in the future has the potential to impact the methane hydrate reservoir in sediments at greater depths along the slope. Thus, this study provides a strong foundation and the necessary characterization of the background state of seepage at the upper limit of methane hydrate stability for future investigations of this important process.« less

Extraction of Seabed/Subsurface Features in a Potential CO2 Sequestration Site in the Southern Baltic Sea, Using Wavelet Transform of High-resolution Sub-Bottom Profiler Data

NASA Astrophysics Data System (ADS)

Tegowski, J.; Zajfert, G.

2014-12-01

Carbon Capture & Storage (CCS) efficiently prevents the release of anthropogenic CO2 into the atmosphere. We investigate a potential site in the Polish Sector of the Baltic Sea (B3 field site), consisting in a depleted oil and gas reservoir. An area ca. 30 x 8 km was surveyed along 138 acoustic transects, realised from R/V St. Barbara in 2012 and combining multibeam echosounder, sidescan sonar and sub-bottom profiler. Preparation of CCS sites requires accurate knowledge of the subsurface structure of the seafloor, in particular deposit compactness. Gas leaks in the water column were monitored, along with the structure of upper sediment layers. Our analyses show the shallow sub-seabed is layered, and quantified the spatial distribution of gas diffusion chimneys and seabed effusion craters. Remote detection of gas-containing surface sediments can be rather complex if bubbles are not emitted directly into the overlying water and thus detectable acoustically. The heterogeneity of gassy sediments makes conventional bottom sampling methods inefficient. Therefore, we propose a new approach to identification, mapping, and monitoring of potentially gassy surface sediments, based on wavelet analysis of echo signal envelopes of a chirp sub-bottom profiler (EdgeTech SB-0512). Each echo envelope was subjected to wavelet transformation, whose coefficients were used to calculate wavelet energies. The set of echo envelope parameters was input to fuzzy logic and c-means algorithms. The resulting classification highlights seafloor areas with different subsurface morphological features, which can indicate gassy sediments. This work has been conducted under EC FP7-CP-IP project No. 265847: Sub-seabed CO2 Storage: Impact on Marine Ecosystems (ECO2).

Three Dimensional Underwater Sound Propagation Over Sloping Bottoms

NASA Astrophysics Data System (ADS)

Glegg, Stewart A. L.; Riley, J. M.

This article reviews the work which has been carried out over the past few years on three dimensional underwater sound propagation over sloping bottoms. When sound propagates across a slope three dimensional effects can cause shadow zones and mode cut off effects to occur, which could not be predicted by a two dimensional model. For many years the theory for this type of propagation over realistic ocean floors, which can support both compressional and shear waves, eluded workers in this field. Recently the complete solution for the acoustic field in a "wedge domain with penetrable boundaries" has been developed, and this has allowed for complete understanding of three dimensional bottom interacting sound propagation. These theories have been verified by a series of laboratory scale experiments and excellent agreement has been obtained. However only one full scale ocean experiment has been carried out on three dimensional, bottom interacting, acoustic propagation. This showed significant horizontal refraction of sound propagating across a continental slope and further verifies the importance of bottom slopes on underwater sound propagation.

50 kHz bottom backscattering measurements from two types of artificially roughened sandy bottoms

NASA Astrophysics Data System (ADS)

Son, Su-Uk; Cho, Sungho; Choi, Jee Woong

2016-07-01

Laboratory measurements of 50 kHz bottom backscattering strengths as a function of grazing angle were performed on the sandy bottom of a water tank; two types of bottom roughnesses, a relatively smooth interface and a rough interface, were created on the bottom surface. The roughness profiles of the two interface types were measured directly using an ultrasound arrival time difference of 5 MHz and then were Fourier transformed to obtain the roughness power spectra. The measured backscattering strengths increased from -29 to 0 dB with increasing grazing angle from 35 to 86°, which were compared to theoretical backscattering model predictions. The comparison results implied that bottom roughness is a key factor in accurately predicting bottom scattering for a sandy bottom.

Characterization of a Louisiana Bay Bottom

NASA Astrophysics Data System (ADS)

Freeman, A. M.; Roberts, H. H.

2016-02-01

This study correlates side-scan sonar and CHIRP water bottom-subbottom acoustic amplitudes with cone penetrometer data to expand the limited understanding of the geotechnical properties of sediments in coastal Louisiana's bays. Standardized analysis procedures were developed to characterize the bay bottom and shallow subsurface of the Sister Lake bay bottom. The CHIRP subbottom acoustic data provide relative amplitude information regarding reflection horizons of the bay bottom and shallow subsurface. An amplitude analysis technique was designed to identify different reflectance regions within the lake from the CHIRP subbottom profile data. This amplitude reflectivity analysis technique provides insight into the relative hardness of the bay bottom and shallow subsurface, useful in identifying areas of erosion versus deposition from storms, as well as areas suitable for cultch plants for state oyster seed grounds, or perhaps other restoration projects. Side-scan and CHIRP amplitude reflectivity results are compared to penetrometer data that quantifies geotechnical properties of surface and near-surface sediments. Initial results indicate distinct penetrometer signatures that characterize different substrate areas including soft bottom, storm-deposited silt-rich sediments, oyster cultch, and natural oyster reef areas. Although amplitude analysis of high resolution acoustic data does not directly quantify the geotechnical properties of bottom sediments, our analysis indicates a close relationship. The analysis procedures developed in this study can be applied in other dynamic coastal environments, "calibrating" the use of synoptic acoustic methods for large-scale water bottom characterization.

The study of the stress - strain state of the tank with bottom water drainage during operation

NASA Astrophysics Data System (ADS)

Shchipkova, Yu V.; Tokarev, V. V.

2018-04-01

Bottom drainage from tank is a current problem in modern tank usage. This article proposes the use of the bottom drainage system from the tank with the shape of the sloped cone to the centre of it. Changing the bottom design alters the stress - strain state to be analyzed in the Ansys. The analysis concluded that the proposed drainage system should be applied.

Reconstructing Holocene palaeo-environmental conditions in the Baltic: A multi-proxy comparison from the Little Belt (IODP Expedition 347, Site M0059)

NASA Astrophysics Data System (ADS)

Kotthoff, Ulrich; Andrén, Elinor; Andrén, Thomas; Ash, Jeanine; Bauersachs, Thorsten; Fanget, Anne-Sophie; Granoszewski, Wojciech; Groeneveld, Jeroen; Krupinski, Nadine; Peyron, Odile; Slomp, Caroline; Stepanova, Anna; Warnock, Jonathan; van Helmond, Niels; Expedition 347 Science Party

2016-04-01

Some of the largest marine environmental impacts from ongoing global climate change are occurring in continental shelf seas and enclosed basins, including severe oxygen depletion, intensifying stratification, and increasing temperatures. In order to predict future changes in water mass conditions, it is essential to reconstruct how these conditions have changed in the past against the background of climate changes. The brackish Baltic Sea is one of the largest semi-enclosed basins worldwide, and its sediment records provide a unique opportunity to analyse palaeo-environmental and climate change in central and northern Europe. IODP Expedition 347 recovered an exceptional set of sediment cores from the Baltic Sea which allow high-resolution reconstructions in unprecedented quality. We present a comparison of commonly-used proxies to reconstruct palaeoecosystems, -temperatures, and -salinity from IODP Site M0059 in the Little Belt over the past ˜8000 years. Our aim is to reconstruct the development of the terrestrial and marine ecosystems in the research area and the related environmental conditions, and to identify potential limitations of individual proxies. The age model for Site M0059 is based on 14Cdating, biostratigraphic correlation with neighbouring terrestrial pollen records, and sediment stratigraphy. Sedimentary organic carbon content and the bulk elemental composition have been measured, and can be used to determine the depositional environment and degree of oxygen depletion (e.g., Mo, Corg/Ptot). Pollen is used as proxy for vegetation development in the hinterland of the southern Baltic Sea and as a land/air-temperature proxy. Comparison with dinoflagellate cysts, insect remains, and green algae remains from the same samples provides a direct land-sea comparison. The application of the modern analogues technique to pollen assemblages has previously yielded precise results for late Pleistocene and Holocene datasets, including specific information on seasonality, but pollen-based reconstructions for Northern Europe may be hampered by plant migration effects. Palynomorph analyses are therefore complemented with analyses of lipid palaeothermometers, such as TEX86 and the long chain diol index (LDI), to reconstruct variations in Baltic Sea surface temperatures (SST). In addition, the MBT/CBT proxy is used to infer past changes in mean annual air temperatures (MAAT). Benthic foraminiferal δ18O and δ13C measurements (monospecific) and foraminifera and ostracod faunal assemblage analyses allow us to estimate bottom water salinity and environmental changes qualitatively and quantitatively. Low bottom water salinity (˜23 in bottom waters) and varying diagenesis in the Little Belt's organic-rich sediments complicates the application of benthic foraminiferal Mg/Ca as a palaeotemperature proxy. Reliable bottom water temperatures, however, are reconstructed using clumped isotope analyses of mollusc material. In addition, diatoms and the diol index (DI) are analysed to determine variation in salinity of the Baltic Sea's surface waters over the investigated time period. The results of this inter-proxy comparison study will be used to reconstruct gradients between different settings, e.g. how water column stratification developed, possibly if and how changes in seasonality occurred, and to identify the circumstances under which specific proxies may be affected by secondary impacts.

Mapping of sea bottom topography

NASA Technical Reports Server (NTRS)

Calkoen, C. J.; Wensink, G. J.; Hesselmans, G. H. F. M.

1992-01-01

Under suitable conditions the bottom topography of shallow seas is visible in remote sensing radar imagery. Two experiments were performed to establish which remote sensing technique or combination yields optimal imaging of bottom topography and which hydro-meteorological conditions are favorable. A further goal is to gain experience with these techniques. Two experiments were performed over an area in the North Sea near the measuring platform Meetpost Noordwijk (MPN). The bottom topography in the test area is dominated by sand waves. The crests of the sand waves are perpendicular to the coast line and the dominating (tidal-)current direction. A 4x4 sq km wide section of the test area was studied in more detail. The first experiment was undertaken on 16 Aug. 1989. During the experiment the following remote sensing instruments were used: Landsat-Thematic Mapper, and NASA/JPL Airborne Imaging Radar (AIR). The hydro-meteorological conditions; current, wind, wave, and air and water temperature were monitored by MPN, a ship of Rijkswaterstaat (the OCTANS), and a pitch-and-roll WAVEC-buoy. The second experiment took place on 12 July 1992. During this experiment data were collected with the NASA/JPL polarimetric synthetic aperture radar (SAR), and a five-band helicopter-borne scatterometer. Again the hydro-meteorological conditions were monitored at MPN and the OCTANS. Furthermore, interferometric radar data were collected.

Mid-depth respired carbon storage and oxygenation of the eastern equatorial Pacific over the last 25,000 years

NASA Astrophysics Data System (ADS)

Umling, Natalie E.; Thunell, Robert C.

2018-06-01

A growing body of evidence suggests that respired carbon was stored in mid-depth waters (∼1-3 km) during the last glacial maximum (LGM) and released to the atmosphere from upwelling regions during deglaciation. Decreased ventilation, enhanced productivity, and enhanced carbonate dissolution are among the mechanisms that have been cited as possible drivers of glacial CO2 drawdown. However, the relative importance of each of these mechanisms is poorly understood. New approaches to quantitatively constrain bottom water carbonate chemistry and oxygenation provide methods for estimating historic changes in respired carbon storage. While increased CO2 drawdown during the LGM should have resulted in decreased oxygenation and a shift in dissolved inorganic carbon (DIC) speciation towards lower carbonate ion concentrations, this is complicated by the interplay of carbonate compensation, export productivity, and circulation. To disentangle these processes, we use a multiproxy approach that includes boron to calcium (B/Ca) ratios of the benthic foraminifera Cibicidoides wuellerstorfi to reconstruct deep-water carbonate ion concentrations ([CO32-]) and the uranium to calcium (U/Ca) ratio of foraminiferal coatings in combination with benthic foraminiferal carbon isotopes to reconstruct changes in bottom water oxygen concentrations ([O2]) and organic carbon export. Our records indicate that LGM [CO32-] and [O2] was reduced at mid water depths of the eastern equatorial Pacific (EEP), consistent with increased respired carbon storage. Furthermore, our results suggest enhanced mixing of lower Circumpolar Deep Water (LCDW) to EEP mid water depths and provide evidence for the importance of circulation for oceanic-atmospheric CO2 exchange.

Geoacoustic inversion of a shallow fresh-water environment

NASA Astrophysics Data System (ADS)

Stotts, Steven A.; Knobles, David P.; Koch, Robert A.; Piper, James N.; Keller, Jason A.

2003-10-01

A recent experiment was conducted at The University of Texas/Applied Research Laboratories test station located at Lake Travis, Austin, TX. Implosive (light bulb), explosive (firecracker), and tonal sources were recorded on a dual receiver system located on the bottom next to a range-independent underwater river channel. Inversion results of the broadband time series obtained over ranges less than 1.5 km were used to predict measured transmission loss at several tonal frequencies in the band from 250-1000 Hz. The average water depth was approximately 38 m along the channel during the experiment. Sound speed profiles were calculated from recorded temperature readings measured as a function of depth. Implosive source spectrums were measured and used to evaluate a model/data correlation cost function in a simulated annealing algorithm. Comparisons of inversion results using both a normal mode and a ray-based plane wave reflection coefficient forward model [Stotts et al., J. Acoust. Soc. Am. (submitted)] are discussed. Predicted transmission loss based on the inversion results are compared to the measured transmission loss. Differences between fluid and elastic layer bottom models will also be presented.

Nutrient Enrichment Drives Gulf of Mexico Hypoxia

NASA Astrophysics Data System (ADS)

Boesch, Donald F.; Boynton, Walter R.; Crowder, Larry B.; Diaz, Robert J.; Howarth, Robert W.; Mee, Laurence D.; Nixon, Scott W.; Rabalais, Nancy N.; Rosenberg, Rutger; Sanders, James G.; Scavia, Donald; Turner, R. Eugene

2009-04-01

During most summers over the past 30 years, bottom dissolved oxygen across a large area of the Louisiana and upper Texas continental shelf declined to concentrations too low (hypoxia) for most fish and large invertebrate animals to survive. This area is one of the best known “dead zones” proliferating around the world [Diaz and Rosenberg, 2008]. During July 2008, hypoxic bottom waters extended across 20,720 square kilometers (Figure 1), but they were probably even more extensive because winds from Hurricane Dolly mixed the waters off Texas before the survey could be completed. Increased inputs of nutrients (principally nitrogen and phosphorus) from the U.S. agricultural heartland within the Mississippi-Atchafalaya River Basin (MARB) are implicated in the development and spread of hypoxia in the Gulf of Mexico. Consequently, the causes of, and solutions for, hypoxia have been subjects of extensive debate and analysis. An integrated scientific assessment led to a 2001 Action Plan [Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, 2001] with a goal of reducing the area of the hypoxic zone to less than 5000 square kilometers by reducing nitrogen loading [Rabalais et al., 2007].

Modelization of highly nonlinear waves in coastal regions

NASA Astrophysics Data System (ADS)

Gouin, Maïté; Ducrozet, Guillaume; Ferrant, Pierre

2015-04-01

The proposed work deals with the development of a highly non-linear model for water wave propagation in coastal regions. The accurate modelization of surface gravity waves is of major interest in ocean engineering, especially in the field of marine renewable energy. These marine structures are intended to be settled in coastal regions where the effect of variable bathymetry may be significant on local wave conditions. This study presents a numerical model for the wave propagation with complex bathymetry. It is based on High-Order Spectral (HOS) method, initially limited to the propagation of non-linear wave fields over flat bottom. Such a model has been developed and validated at the LHEEA Lab. (Ecole Centrale Nantes) over the past few years and the current developments will enlarge its application range. This new numerical model will keep the interesting numerical properties of the original pseudo-spectral approach (convergence, efficiency with the use of FFTs, …) and enable the possibility to propagate highly non-linear wave fields over long time and large distance. Different validations will be provided in addition to the presentation of the method. At first, Bragg reflection will be studied with the proposed approach. If the Bragg condition is satisfied, the reflected wave generated by a sinusoidal bottom patch should be amplified as a result of resonant quadratic interactions between incident wave and bottom. Comparisons will be provided with experiments and reference solutions. Then, the method will be used to consider the transformation of a non-linear monochromatic wave as it propagates up and over a submerged bar. As the waves travel up the front slope of the bar, it steepens and high harmonics are generated due to non-linear interactions. Comparisons with experimental data will be provided. The different test cases will assess the accuracy and efficiency of the method proposed.

Innovative Technique for High-Accuracy Remote Monitoring of Surface Water

NASA Astrophysics Data System (ADS)

Gisler, A.; Barton-Grimley, R. A.; Thayer, J. P.; Crowley, G.

2016-12-01

Lidar (light detection and ranging) provides absolute depth and topographic mapping capability compared to other remote sensing methods, which is useful for mapping rapidly changing environments such as riverine systems and agricultural waterways. Effectiveness of current lidar bathymetric systems is limited by the difficulty in unambiguously identifying backscattered lidar signals from the water surface versus the bottom, limiting their depth resolution to 0.3-0.5 m. Additionally these are large, bulky systems that are constrained to expensive aircraft-mounted platforms and use waveform-processing techniques requiring substantial computation time. These restrictions are prohibitive for many potential users. A novel lidar device has been developed that allows for non-contact measurements of water depth down to 1 cm with an accuracy and precision of < 1 cm by exploiting the polarization properties of the light-surface interaction. This system can transition seamlessly from ranging over land to shallow to deep water allowing for shoreline charting, measuring water volume, mapping bottom topology, and identifying submerged objects. The scalability of the technique opens up the ability for handheld or UAS-mounted lidar bathymetric systems, which provides for potential applications currently unavailable to the community. The high laser pulse repetition rate allows for very fine horizontal resolution while the photon-counting technique permits real-time depth measurement and object detection. The enhanced measurement capability, portability, scalability, and relatively low-cost creates the opportunity to perform frequent high-accuracy monitoring and measuring of aquatic environments which is crucial for monitoring water resources on fast timescales. Results from recent campaigns measuring water depth in flowing creeks and murky ponds will be presented which demonstrate that the method is not limited by rough water surfaces and can map underwater topology through moderately turbid water.

Far-field tsunami magnitude determined from ocean-bottom pressure gauge data around Japan

NASA Astrophysics Data System (ADS)

Baba, T.; Hirata, K.; Kaneda, Y.

2003-12-01

\\hspace*{3mm}Tsunami magnitude is the most fundamental parameter to scale tsunamigenic earthquakes. According to Abe (1979), the tsunami magnitude, Mt, is empirically related to the crest to trough amplitude, H, of the far-field tsunami wave in meters (Mt = logH + 9.1). Here we investigate the far-field tsunami magnitude using ocean-bottom pressure gauge data. The recent ocean-bottom pressure measurements provide more precise tsunami data with a high signal-to-noise ratio. \\hspace*{3mm}Japan Marine Science and Technology Center is monitoring ocean bottom pressure fluctuations using two submarine cables of depths of 1500 - 2400 m. These geophysical observatory systems are located off Cape Muroto, Southwest Japan, and off Hokkaido, Northern Japan. The ocean-bottom pressure data recorded with the Muroto and Hokkaido systems have been collected continuously since March, 1997 and October, 1999, respectively. \\hspace*{3mm}Over the period from March 1997 to June 2003, we have observed four far-field tsunami signals, generated by earthquakes, on ocean-bottom pressure records. These far-field tsunamis were generated by the 1998 Papua New Guinea eq. (Mw 7.0), 1999 Vanuatu eq. (Mw 7.2), 2001 Peru eq. (Mw 8.4) and 2002 Papua New Guinea eq. (Mw 7.6). Maximum amplitude of about 30 mm was recorded by the tsunami from the 2001 Peru earthquake. \\hspace*{3mm}Direct application of the Abe's empirical relation to ocean-bottom pressure gauge data underestimates tsunami magnitudes by about an order of magnitude. This is because the Abe's empirical relation was derived only from tsunami amplitudes with coastal tide gauges where tsunami is amplified by the shoaling of topography and the reflection at the coastline. However, these effects do not work for offshore tsunami in deep oceans. In general, amplification due to shoaling near the coastline is governed by the Green's Law, in which the tsunami amplitude is proportional to h-1/4, where h is the water depth. Wave amplitude also is doubled by reflection at the fixed edge (coastline). Hence, we introduce a water-depth term and a reflection coefficient of 2 in the original Abe_fs empirical relation to correct tsunami amplitude for open oceans and obtain Mt = log(2H/h-1/4) + 9.1, where h is the depth of the ocean bottom pressure gage. The modified empirical relation produces tsunami magnitudes close to those determined using tide gauges.

Water-quality data from shallow pond-bottom groundwater in the Fishermans Cove area of Ashumet Pond, Cape Cod, Massachusetts, 2001–2010

USGS Publications Warehouse

McCobb, Timothy D.; LeBlanc, Denis R.

2011-01-01

The U.S. Geological Survey (USGS) collected water-quality data between 2001 and 2010 in the Fishermans Cove area of Ashumet Pond, Falmouth, Massachusetts, where the eastern portion of a treated-wastewater plume, created by more than 60 years of overland disposal, discharges to the pond. Temporary drive points were installed, and shallow pond-bottom groundwater was sampled, at 167 locations in 2001, 150 locations in 2003, and 120 locations in 2004 to delineate the distribution of wastewater-related constituents. In 2004, the Air Force Center for Engineering and the Environment (AFCEE) installed a pond-bottom permeable reactive barrier (PRB) to intercept phosphate in the plume at its discharge point to the pond. The USGS monitored the performance of the PRB by collecting samples from temporary drive points at multiple depth intervals in 2006 (200 samples at 76 locations) and 2009 (150 samples at 90 locations). During the first 5 years after installation of the PRB, water samples were collected periodically from five types of pore-water samplers that had been permanently installed in and near the PRB during the barrier's emplacement. The distribution of wastewater-related constituents in the pond-bottom groundwater and changes in the geochemistry of the pond-bottom groundwater after installation of the PRB have been documented in several published reports that are listed in the references.

Nuclear Fuel Traces Definition in Storage Ponds of Research VVR-2 and OR Reactors in NRC 'Kurchatov Institute'

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stepanov, Alexey; Simirskii, Iurii; Stepanov, Vyacheslav

2015-07-01

The Gas Plant complex is the experimental base of the Institute of Nuclear Reactors, which is part of the Kurchatov Institute. In 1954 the commissioning of the first Soviet water-cooled water-moderated research reactor VVR-2 on enriched uranium, and until 1983 the complex operated two research water-cooled water-moderated reactors 3 MW (VVR-2) and 300 kW (OR) capacity, which were dismantled in connection with the overall upgrades of the complex. The complex has three storage ponds in the reactor building. They are sub-surface vessels filled with water (the volume of water in each is about 6 m{sup 3}). In 2007-2013 the spentmore » nuclear fuel from storages was removed for processing to 'Mayk'. Survey of Storage Ponds by Underwater Collimated Spectrometric System shows a considerable layer of slime on the bottom of ponds and traces of spent nuclear fuel in one of the storage. For determination qualitative and the quantitative composition of radionuclide we made complex α-, β-, γ- spectrometric research of water and bottom slimes from Gas Plant complex storage ponds. We found the spent nuclear fuel in water and bottom slime in all storage ponds. Specific activity of radionuclides in the bottom slime exceeded specific activity of radionuclides in the ponds water and was closed to levels of high radioactive waste. Analysis of the obtained data and data from earlier investigation of reactor MR storage ponds showed distinctions of specific activity of uranium and plutonium radionuclides. (authors)« less

Cibicidodes Pachyderma B/Ca as a Shalow Water Carbonate Saturation State Proxy

NASA Astrophysics Data System (ADS)

Wojcieszek, D. E.; Flower, B. P.; Moyer, R. P.; Byrne, R. H.

2012-12-01

Since the industrial revolution, the oceans have absorbed about 25% of anthropogenic CO2 emissions to the atmosphere, leading to a decrease in seawater pH (termed ocean acidification: OA) as well as many associated effects, including decreased saturation states. Assessment of the effects of OA on marine ecosystems is presently based on <50 years of observations. Reconstructions of past seawater chemistry and its impact on biota over much longer time scales can provide essential context for likely future consequences of OA. Reliable oceanic paleo-proxies for influential chemical variables such as pH and carbonate saturation state are crucial components for examining ancient environments affected by OA. Addition of CO2 to seawater leads to not only decreases in seawater pH and saturation state, but also the extent to which boron (B) is incorporated into CaCO3 during biotic calcification. Consequently, the abundance of B in calcite could reflect pH and/or saturation state of the water in which calcification occurred. Recent studies indicate a linear relationship between the ratio of boron to calcium (B/Ca) in benthic foraminifera shells ( Cibicidoides wuellerstorfi, C. mundulus) and the degree of carbonate saturation (Δ[CO32-]), defined as a difference between [CO32-]in situ and [CO32-]saturation. However, the observed relationship between B/Ca and Δ[CO32-] was only established for depths >1000m. Thus, since OA most immediately affects the upper 1000 m of the water column, a reliable shallow water (<1000 m) carbonate chemistry proxy is desirable. We are testing the utility of B/Ca in Cibicidoides pachyderma as a shallow water Δ[CO32-] proxy. C. pachyderma is an epibenthic species and therefore records the composition of bottom, rather than interstitial, waters. It usually inhabits depths between 200 and 1000 m, and is a common species in the Gulf of Mexico. The gently sloping West Florida Shelf (WFS) is an excellent setting for this kind of study as it provides a full range of depths habitable by C.pachyderma. Nine surface sediment samples were collected along a 150-1400 m depth transect across the WFS. Bottom water pH along the transect ranged between 7.82 and 8.12, corresponding to Δ[CO32-] values between 35 and 200 μmol/kg. Preliminary B/Ca data range between 109 and 174 μmol/mol and display high variability. Our results suggest that WFS bottom water chemistry may be intermittently affected by phenomena such as eutrophication-induced hypoxia or boundary layer differences between the lower water column and the sediment-water interface. Additional B/Ca and bottom water measurements are planned to characterize the relationship between C.pachyderma B/Ca and Δ[CO32-], and extend global benthic foraminifera B/Ca calibrations to depths shallower than 1000 m.

Chromium distribution in an Amazonian river exposed to tannery effluent.

PubMed

de Sousa, Eduardo Araujo; Luz, Cleber Calado; de Carvalho, Dario Pires; Dorea, Caetano Chang; de Holanda, Igor Bruno Barbosa; Manzatto, Ângelo Gilberto; Bastos, Wanderley Rodrigues

2016-11-01

This study aims to evaluate the Cr concentrations in surface water, suspended particles, and bottom sediments exposed to tannery effluent releases in the Candeias River. Cr concentrations were compared in relation to environmental thresholds imposed by United States Environmental Protection Agency (USEPA) and the Brazilian Environmental Council (CONAMA), and the geoaccumulation index (Igeo) was calculated in bottom sediment. Samples were collected in flood and dry seasons. Cr extraction was done by an acid extraction and quantified by flame atomic absorption spectrometry. Most samples were found to be below the environmental thresholds imposed by CONAMA and USEPA, except in the one from the discharge zone sampled during the dry season, showing values 1.5 and 6.1 higher than CONAMA in water and bottom sediment, respectively. Cr concentrations were significantly higher (P < 0.001) in suspended particles during dry season than flood season. Surface water and bottom sediment did not show significant differences between the seasons. The Igeo revealed an enrichment of Cr in bottom sediments after discharge zone, indicating that the effluent may be contributing to metal accumulation in the sediment. Apparently, the Candeias River shows a wash behavior on the river bottom, leaching the accumulated metal deposited on the riverbed to other areas during the flood pulses, which decreases Cr concentration in the discharge zone during dry seasons. Thus, this behavior can promote Cr dispersion to unpolluted areas.

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

USGS Publications Warehouse

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

1977-01-01

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.

Effects of tides on the cross-isobath movement of the low-salinity plume in the western Yellow and East China Seas in winter

NASA Astrophysics Data System (ADS)

Wang, Bin; Hirose, Naoki; Yuan, Dongliang; Moon, Jae-Hong; Pan, Xishan

2017-07-01

Offshore extension of the fresh Subei coast water is identified in winter based on in site salinity observation data in this and previous studies. A high-resolution regional ocean circulation model is used to investigate the cross-isobath movement of low salinity-water over the Yellow and East China Seas, and it has reproduced the salinity distribution observed in the winter of 2014-2015 successfully. The model suggests that the low-salinity water is basically degenerated back to the eastern coast of China in winter because of strong northeasterly wind. However, a part of the low-salinity water extends offshore in the southeast direction across the 20-50 m isobaths over the Yangtze Bank, which cannot be explained by either the northerly winter monsoon or the Changjiang discharge. Numerical experiments suggest that the cross-isobath transport of the soluble substances is highly attributed to the tidal residual current, flowing southeastward across 20-50 m isobaths over the whole Yangtze Bank. The results of controlled experiments also indicate that the bottom shear of the tidal current, rather than the tidal mixing, plays a significant role in the cross-isobath current during winter.

Spatial and temporal variation of acoustic backscatter in the STRESS experiment

NASA Astrophysics Data System (ADS)

Dworski, J. George; Jackson, Darrell R.

1994-08-01

Acoustic backscatter measurements were made of the seabed with a bottom mounted, circularly scanning sonar. The placement was at 91 m depth, mid-shelf of Northern California (38° 34'N), site C3 of the experiment STRESS I (1988-1989). Our expectation was that sonar images (70 m radius, 12,000 m 2) would provide a means of observing, over a large field of view, changes in the bottom due to storm-induced sediment transport and due to bioturbation. This expectation was supported in part by towed sonar measurements at 35 kHz over a sandy area in the North Sea, where dramatic spatial variation in the level of the backseattered signal was observed during an Autumn storm on scales of a few km with no concomitant change in sediment grain size [ JACKSONet al. (1986) The Journal of the Acoustical Society of America, 80, 1188-1199]. It appeared possible that storm-driven sediment transport might have been responsible for this patchiness, by altering bottom roughness and by redeposition of suspended material. At the California site, a conventional sonar processing of our data from the STRESS experiment reveals no such dramatic change in backscattered signal level due to storms. The sonar images contain random structures whose time evolution is subtle and difficult to interpret. A much clearer picture of temporal and spatial variations emerges from a processing scheme involving cross-correlation of time-separated acoustic views of the bottom. In effect, the sequence of correlation data images produces a movie in which patches of activity are seen to develop as functions of time. It appears that most of this activity is biological rather than hydrodynamic. A tentative explanation is two-fold. The bottom shear stress might have been considerably greater at the North Sea site (with depth only one-half of the California site). The seafloor at the California site was silty-clayey, and backscatter from such floor is less sensitive to the water-floor interface shape and roughness than it would be to the same parameters of a sandy bottom.

Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water

PubMed Central

van Wijk, Esmee

2018-01-01

Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise. PMID:29675467

Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water.

PubMed

Silvano, Alessandro; Rintoul, Stephen Rich; Peña-Molino, Beatriz; Hobbs, William Richard; van Wijk, Esmee; Aoki, Shigeru; Tamura, Takeshi; Williams, Guy Darvall

2018-04-01

Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.

Analyses of native water, bottom material, elutriate samples, and dredged material from selected southern Louisiana waterways and selected areas in the Gulf of Mexico, 1979-81

USGS Publications Warehouse

Lurry, Dee L.

1983-01-01

The U.S. Geological Survey was requested by the U.S. Army Corps of Engineers, New Orleans District, to provide water-quality data to evaluate environmental effects of dredging activities in selected reaches of the Calcasieu River in southwestern Louisiana. Samples were collected from the upper and lower Calcasieu River between January 1980 and March 1981. Thirty-three samples (22 native-water and 11 effluent) were collected from eleven dredging sites. In addition, a series of elutriate studies were conducted between July 1979 and July 1981 to determine water quality as a basis for assessing possible environmental effects of proposed dredging activities in the following areas: Grand Bayou and Martins Canal near Happy Jack, unnamed bayou near Port Sulphur, Grand Bayou and Pipeline Canal near Port Sulphur and Bayou des Plantins near Empire; Mississippi River Gulf Outlet and Inner Harbor Navigation Canal; Southwest Pass; Barataria Bay; Atchafalaya Bay at Eugene Island; Calcasieu Ship Channel. Samples of native water and samples of bottom material were collected from 22 different sites and elutriate (mixtures of native water and bottom material) samples were prepared and analyzed. Four proposed ocean-disposal sites were sampled for bottom material only. Samples were analyzed for selected chemical and biological constituents and physical properties. (USGS)

Isolation and identification of Pathogenic Naegleria from Florida lakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wellings, F.M.; Amuso, P.T.; Chang, S.L.

1977-12-01

Five cases of primary amoebic meningoencephalitis associated with swimming in freshwater lakes have been recorded in Florida over the past 14 years. The present study demonstrated that pathogenic naegleria, the causative agent, is relatively widespread. Twelve of 26 lakes sampled only once yielded the amoeba. Populations in three of five lakes sampled routinely reached levels of one amoeba per 25 ml of water tested during the hot summer months. Overwintering in freshwater lake bottom sediments was demonstrated, showing that thermal-discharge pollution of waters plays a miniscule, if any, role in the maintenance of pathogenic naegleria in nature in this semitropicalmore » area.« less

An acoustic backscatter thermometer for remotely mapping seafloor water temperature

NASA Astrophysics Data System (ADS)

Jackson, Darrell R.; Dworski, J. George

1992-01-01

A bottom-mounted, circularly scanning sonar operating at 40 kHz has been used to map changes in water sound speed over a circular region 150 m in diameter. If it is assumed that the salinity remains constant, the change in sound speed can be converted to a change in temperature. For the present system, the spatial resolution is 7.5 m and the temperature resolution is 0.05°C. The technique is based on comparison of successive sonar scans by means of a correlation algorithm. The algorithm is illustrated using data from the Sediment Transport Events on Slopes and Shelves (STRESS) experiment.

An Expendable Source for Measuring Shallow Water Acoustic Propagation and Geo-Acoustic Bottom Properties

DTIC Science & Technology

2015-09-30

Propagation and Geo -Acoustic Bottom Properties Harry A DeFerrari RSMAS – University of Miami 4600 Rickenbacker Causeway Miami FL. 33149...limited information about the ocean acoustic environment and the geo -acoustic properties of the bottom. The objective here is to measure the pulse...models and estimate the geo -acoustic properties of the bottom by inversion. APPROACH M-sequences have long been the workhorse of basic research

A comparison of waveform processing algorithms for single-wavelength LiDAR bathymetry

NASA Astrophysics Data System (ADS)

Wang, Chisheng; Li, Qingquan; Liu, Yanxiong; Wu, Guofeng; Liu, Peng; Ding, Xiaoli

2015-03-01

Due to the low-cost and lightweight units, single-wavelength LiDAR bathymetric systems are an ideal option for shallow-water (<12 m) bathymetry. However, one disadvantage of such systems is the lack of near-infrared and Raman channels, which results in difficulties in extracting the water surface. Therefore, the choice of a suitable waveform processing method is extremely important to guarantee the accuracy of the bathymetric retrieval. In this paper, we test six algorithms for single-wavelength bathymetric waveform processing, i.e. peak detection (PD), the average square difference function (ASDF), Gaussian decomposition (GD), quadrilateral fitting (QF), Richardson-Lucy deconvolution (RLD), and Wiener filter deconvolution (WD). To date, most of these algorithms have previously only been applied in topographic LiDAR waveforms captured over land. A simulated dataset and an Optech Aquarius dataset were used to assess the algorithms, with the focus being on their capability of extracting the depth and the bottom response. The influences of a number of water and equipment parameters were also investigated by the use of a Monte Carlo method. The results showed that the RLD method had a superior performance in terms of a high detection rate and low errors in the retrieved depth and magnitude. The attenuation coefficient, noise level, water depth, and bottom reflectance had significant influences on the measurement error of the retrieved depth, while the effects of scan angle and water surface roughness were not so obvious.

Ground-water, surface-water, and bottom-sediment contamination in the O-field area, Aberdeen Proving Ground, Maryland, and the possible effects of selected remedial actions on ground water

USGS Publications Warehouse

Vroblesky, Don A.; Lorah, Michelle M.; Oliveros, James P.

1995-01-01

Disposal of munitions and chemical-warfare substances has introduced inorganic and organic contaminants to the ground water, surface water, and bottom sediment at O-Field, in the Edgewood area of Aberdeen Proving Ground, Maryland. Contaminants include chloride, arsenic, transition metals, chlorinated aliphatic hydrocarbons, aromatic compounds, and organosulfur and organophosphorus compounds. The hydrologic effects of several remedial actions were estimated by use of a ground-water-flow model. The remedial actions examined were an impermeable covering, encapsulation, subsurface barriers, a ground-water drain, pumping of wells to manage water levels or to remove contaminated ground water for treatment, and no action.

The utility of Skylab photo-interpreted earth resources data in studies of marine geology and coastal processes in Puerto Rico and the Virgin Islands

NASA Technical Reports Server (NTRS)

Trumbull, J. V. A. (Principal Investigator)

1975-01-01

The author has identified the following significant results. Three Skylab earth resources passes over Puerto Rico and St. Croix on 6 June and 30 November 1973 and 18 January 1974 resulted in color photography and multispectral photography and scanner imagery. Bathymetric and turbid water features are differentiable by use of the multispectral data. Photography allows mapping of coral reefs, offshore sand deposits, areas of coastal erosion, and patterns of sediment transport. Bottom sediment types could not be differentiated. Patterns of bottom dwelling biologic communities are well portrayed but are difficult to differentiate from bathymetric detail. Effluent discharges and oil slicks are readily detected and are differentiated from other phenomena by the persistence of their images into the longer wavelength multispectral bands.

Implementation of the new hydrographic technologies for bottom topography and seafloor gas venting investigations in the russian northern seas

NASA Astrophysics Data System (ADS)

Koloskov, Evgenii

2017-04-01

The report examines modern hydrographic technologies for the Russian northern seas investigations. The new hydro acoustics methods for seabed study are discussed. It presents stages of seafloor relief studies in the Russian Arctic seas since the 1950s and the obtained results. At the beginning of the 21st century an entirely new phase of bathymetric investigations began with the use of Multibeam Echosounders (MB) and modern hydrographic software. The software tools to process and analyze the bathymetry, and more recently to characterize the seabed from the backscatter, are available in a majority of modern sonar systems. Besides the bathymetry and sonar data, modern MB can produce water column images. These hydrographic technologies provide the possibility to achieve a high level of the seafloor topography. The latest generation of hydrographic MB now has the ability to provide the water column images along with the seafloor. The gas seeps from multibeam water column data can be distantly discerned against the seabed relief background with the aid of the Fledermause software package ("FMMidwater" module). The ability to integrate the water column data with the seafoor and other information,in an integrated geospatial and temporal environment, enhanced the analysis and interpretation of the data which is essential for marine geological research and investigations. The modern hydrographic equipment presents the ability to integrate the MB digital relief models (DTM) and sub bottom profiler data. This provide the possibility to obtain not only the detailed seabed topography, but also the additional information concerning the structure of under bottom soil layers and presence of the endogenous objects in near bottom environment. The importance of the hydrographic software tools needed to process and analyze the bathymetry and water column data are emphasized. The practical importance of the water column and bottom profiler data processing for the submarine gas-hydrates survey is stated. The attention is paid to the implementation of the parametric sub bottom profilers - the low frequency sonar for the sea bottom vertical section investigation. The ability for the integrated presentation of the multibeam bathymetry and vertical curtains in the 3D environment are discussed. As an example of the modern swath survey results achieved with Kongsberg EM2040CD MB and hydrographic information technology QINSy/ Fledermause, are discussed and presented. This survey was performed for the RosNeft company in the Kara sea. Recommendations for the implementation of the multi beam echo sounder and parametric sub bottom profiler for the combined hydrographic and submarine gas-hydrates survey in the Russian northern seas are delivered.The gas-hydrate survey guidelines using MB and QINSy/Fledermause software are provided. The hydrographic software tools used to process and analyze the bathymetry can create the seafloor DTM with the high degree of resolution and provide 3D visualization.These new possibilities provide such realistic view of the sea bottom relief and environment that can be characterized as the marine landscapes. Thus it became possible to investigate the relief morphological peculiarities and obtain the information about the relief genesis. This opens the new opportunities for using the acoustic techniques for varies types of marine activity including the bottom environmental study. The appearance of the bottom thermokarst activity derived from the high resolution DTM generated from the real time MB data is presented. The bottom thermokarst provides the potential threat for underwater pipelines and other submarine communications. The arctic bottom relief peculiarities are also covered including grounded hummock traces and dome-shaped elevations. The investigation of such bottom land forms has become possible recently as the result of implementing the wide swath survey methods. Such unique relief features are in general related to seabed gas venting in the form of the submarine gas-hydrates seeps. The opportunities for investigation of the morphological relief peculiarities and getting the new information is mportant also for varies types of marine activity including the marine ecology study. The arctic sea specific microrelief images are provided to show the abnormality of the bottom surface. The main attention is paid to specific and bottom features such as trenches the grounded hummock traces and dome-shaped elevations of the Pingo-type-unique forms of microrelief usually confined to the bottom gas flow in the form of methane emissions. The attention is also paid to the consequences of the global climate change and its influence on the bottom sole. Key words: hydrographic technologies, hydro acoustics methods, swathe survey, sea bottom vertical section, submarine gas-hydrates, submarine permafrost, seafloor gas venting,multi beam echo sounder, parametric sub bottom profiler.

Short-term environmental impact of clam dredging in coastal waters (south of Portugal): chemical disturbance and subsequent recovery of seabed.

PubMed

Falcão, M; Gaspar, M B; Caetano, M; Santos, M N; Vale, C

2003-12-01

The physical and chemical changes in sediment and near bottom water caused by clam dredging were examined during July and September 1999, at two locations Vilamoura (VL) and Armona (AR), south coast of Portugal. Sediment cores and near bottom water were collected simultaneously before dredging (control samples) and within short time intervals (min-h) after dredging. After dredging operations, microphytobenthos coming from the path were accumulated in the re-worked sediment (ridge). Chlorophyll a in superficial sediment increased from 1.2 microg x g(-1) before dredging to 1.7 microg x g(-1) after dredging and these higher values remained for a few hours. However, the expected increase of chlorophyll a in near bottom water due to re-suspension was not observed. After sediment disturbance an instantaneous sorption of phosphorus onto iron oxides occurred in the upper sediment layers (from 2 to 3 micromol x g(-1) before dredging to 4-5 micromol x g(-1) after dredging). A microcosm experiment showed that after sediment disturbance HPO(4)(2-) dissolved in pore water decreased from 40 to 10 microM being simultaneously sorbed onto iron oxides formed in the top layer of sediment. The ammonium, nitrates, organic nitrogen, phosphate and silicate dissolved in pore water decreased immediately after dredging activity and simultaneously an increase in near bottom water was sporadically observed. Generally, the re-establishment of seabed was reached within a short time (min-h), at both stations (VL and AR).

Field screening of water quality, bottom sediment, and biota associated with irrigation drainage in the Yuma Valley, Arizona, 1995

USGS Publications Warehouse

Tadayon, Saeid; King, K.A.; Andrews, Brenda; Roberts, William

1997-01-01

Because of concerns expressed by the U.S. Congress and the environmental community, the Department of the Interior began a program in late 1985 to identify the nature and extent of water-quality problems induced by irrigation that might exist in the western States. Surface water, bottom sediment, and biota were collected from March through September 1995 along the lower Colorado River and in agricultural drains at nine sites in the Yuma Valley, Arizona, and analyzed for selected inorganic and organic constituents. Analyses of water, bottom sediment, and biota were completed to determine if irrigation return flow has caused, or has the potential to cause, harmful effects on human health, fish, and wildlife in the study area. Concentrations of dissolved solids in surface-water samples collected in March generally did not vary substantially from surface-water samples collected in June. Concentrations of dissolved solids ranged from 712 to 3,000 milligrams per liter and exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level of 500 milligrams per liter for drinking water. Concentrations of chloride in 9 of 18 water samples and concentrations of sulfate in 16 of 18 water samples exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level of 250 milligrams per liter for drinking water. Calcium and sodium were the dominant cations, and chloride and sulfate were the dominant anions. The maximum selenium concentration of 8 micrograms per liter exceeded the U.S. Environmental Protection Agency aquatic-life chronic criterion of 5 micrograms per liter. Concentrations of lead in 7 of 18 water samples and concentrations of mercury in 4 of 18 water samples exceeded the aquatic-life cronic criteria of 3.2 and 0.012 micrograms per liter, respectively. Concentrations of antimony, beryllium, cadmium, and silver in the water samples were below analytical reporting limits. Arsenic was detected in 3 of 9 bottom-sediment samples, and concentrations ranged from 11 to 16 micrograms per gram. Concentrations ofaluminum, beryllium, boron, copper, lead, and zinc were highest in samples from Main Drain at southerly international boundary near San Luis, Arizona. Selenium was detected in all bottom-sediment samples, and concentrations ranged from 0.1 to 0.7 micrograms per gram. Concentrations of cadmium, europium, homium, mercury, molybdenum, silver, tantalum, tin, and uranium were below analytical reporting limits in the bottom-sediment samples. Concentrations of trace elements in bottom-sediment samples were within the ranges found in a study of soils of the western United States and did not indicate a significant accumulation of these constituents. p,p'Dichlorodiphenyldichloroethylene (commonly referred to as p,-p'-DDE) was detected in one bottom-sediment sample at a concentration of 1.4 micrograms per gram. No other organochlorine compounds were detected in the bottom-sediment samples. DDE was present in all fish and bird samples. Almost one-half of the fish samples contained DDE residues that were two times higher than the mean calculated for a national study in 1984-85. Twenty-tree percent of the fish contained more than three times the national mean. Fish from downstream parts of the Main Drain had the highest concentrations of DDE. Although concentrations of DDE in fish and in bird carcasses and eggs were above background levels, residues generally were below thresholds associated with chronic poisoning and reproductive problems in figh and wildlife. Concentrations of 18 trace elements were detected in cattail (Typha sp.) roots, freshwater clam (Corbicula fluminea), fish, and bird samples. Selenium in most fish and in livers of red-winged (Agelaius phoeniceus) and yellow-headed (Xanthocephalus xanthocephalus) blackbirds was above background concentrations but below toxic concentrations. In contrast, selenium was present in a killdeer (Charadrium vociferus) liver sample at potentially toxic con

Water-quality, water-level, and lake-bottom-sediment data collected from the defense fuel supply point and adjacent properties, Hanahan, South Carolina, 1990-96

USGS Publications Warehouse

Petkewich, M.D.; Vroblesky, D.A.; Robertson, J.F.; Bradley, P.M.

1997-01-01

A 9-year scientific investigation to determine the potential for biore-mediation of ground-water contamination and to monitor the effectiveness of an engineered bioremediation system located at the Defense Fuel Supply Point and adjacent properties in Hanahan, S.C., has culminated in the collection of abundant water-quality and water-level data.This report presents the analytical results of the study that monitored the changes in surface- and ground-water quality and water-table elevations in the study area from December 1990 to January 1996. This report also presents analytical results of lake-bottom sediments collected in the study area.

Effect of kaolin addition on the performance of controlled low-strength material using industrial waste incineration bottom ash.

PubMed

Naganathan, Sivakumar; Razak, Hashim Abdul; Hamid, Siti Nadzriah Abdul

2010-09-01

Incineration of industrial waste produces large quantities of bottom ash which are normally sent to secured landfill, but is not a sustainable solution. Use of bottom ash in engineering applications will contribute to sustainability and generate revenue. One way of using the industrial waste incineration bottom ash is in controlled low-strength material (CLSM). Use of bottom ash in CLSM has problems related to bleeding and excessive strength development and so an additive has to be used to control bleeding and strength development. The main objective of this research is to study the effect of kaolin addition on the performance of CLSM made using industrial waste incineration bottom ash. CLSM mixes were made with bottom ash, cement, and refined kaolin. Various tests were performed on the CLSM in fresh and hardened states including compressive strength, water absorption, California bearing ratio (CBR) and the tests for concentration of leachable substances on the bleed and leachate. The compressive strength of CLSM tested ranged from 0.11 to 9.86 MPa. CBR values ranged from 6 to 46, and water absorption values from 12 to 36%. It was shown that the addition of kaolin delayed the initial setting time of CLSM mixtures, reduced bleeding, lowered the compressive strength, and increased the values of water absorption, sorption, and initial surface absorption. The CLSM tested did not have corrosivity. It was shown that the hardened CLSM was non hazardous, and the addition of kaolin increased the concentration of heavy metals and salts in the bleed and leachate.

Assessing prey fish populations in Lake Michigan: Comparison of simultaneous acoustic-midwater trawling with bottom trawling

USGS Publications Warehouse

Fabrizio, Mary C.; Adams, Jean V.; Curtis, Gary L.

1997-01-01

The Lake Michigan fish community has been monitored since the 1960s with bottom trawls, and since the late 1980s with acoustics and midwater trawls. These sampling tools are limited to different habitats: bottom trawls sample fish near bottom in areas with smooth substrates, and acoustic methods sample fish throughout the water column above all substrate types. We compared estimates of fish densities and species richness from daytime bottom trawling with those estimated from night-time acoustic and midwater trawling at a range of depths in northeastern Lake Michigan in summer 1995. We examined estimates of total fish density as well as densities of alewife Alosa pseudoharengus (Wilson), bloater Coregonus hoyi (Gill), and rainbow smelt Osmerus mordax (Mitchell) because these three species are the dominant forage of large piscivores in Lake Michigan. In shallow water (18 m), we detected more species but fewer fish (in fish/ha and kg/ha) with bottom trawls than with acoustic-midwater trawling. Large aggregations of rainbow smelt were detected by acoustic-midwater trawling at 18 m and contributed to the differences in total fish density estimates between gears at this depth. Numerical and biomass densitites of bloaters from all depths were significantly higher when based on bottom trawl samples than on acoustic-midwater trawling, and this probably contributed to the observed significant difference between methods for total fish densities (kg/ha) at 55 m. Significantly fewer alewives per ha were estimated from bottom trawling than from acoustics-midwater trawling at 55 m, and in deeper waters, no alewives were taken by bottom trawling. The differences detected between gears resulted from alewife, bloater, and rainbow smelt vertical distributions, which varied with lake depth and time of day. Because Lake Michigan fishes are both demersal and pelagic, a single sampling method cannot be used to completely describe characteristics of the fish community.

Influence of submarine morphology on bottom water flow across the western Ross Sea continental margin

USGS Publications Warehouse

Davey, F.J.; Jacobs, S.S.

2007-01-01

Multibeam sonar bathymetry documents a lack of significant channels crossing outer continental shelf and slope of the western Ross Sea. This indicates that movement of bottom water across the shelf break into the deep ocean in this area is mainly by laminar or sheet flow. Subtle, ~20 m deep and up to 1000 m wide channels extend down the continental slope, into tributary drainage patterns on the upper rise, and then major erosional submarine canyons. These down-slope channels may have been formed by episodic pulses of rapid down slope water flow, some recorded on bottom current meters, or by sub-ice melt water erosion from an icesheet grounded at the margin. Narrow, mostly linear furrows on the continental shelf thought to be caused by iceberg scouring are randomly oriented, have widths generally less than 400 m and depths less than 30m, and extend to water depths in excess of 600 m.

Turbidity distribution in the Atlantic Ocean

USGS Publications Warehouse

Eittreim, S.; Thorndike, E.M.; Sullivan, L.

1976-01-01

The regional coverage of Lamont nephelometer data in the North and South Atlantic can be used to map seawater turbidity at all depths. At the level of the clearest water, in the mid-depth regions, the turbidity distribution primarily reflects the pattern of productivity in the surface waters. This suggests that the 'background' turbidity level in the oceans is largely a function of biogenic fallout. The bottom waters of the western Atlantic generally exhibit large increases in turbidity. The most intense benthic nepheloid layers are in the southwestern Argentine basin and northern North American basin; the lowest bottom water turbidity in the western Atlantic is in the equatorial regions. Both the Argentine and North American basin bottom waters appear to derive their high turbidity largely from local resuspension of terrigenous input in these basins. In contrast to the west, the eastern Atlantic basins show very low turbidities with the exception of three regions: the Mediterranean outflow area, the Cape basin, and the West European basin. ?? 1976.

Annual subsurface transport of a red tide dinoflagellate to its bloom area: Water circulation patterns and organism distributions in the Chesapeake Bay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tyler, M.A.; Seliger, H.H.

1978-03-01

An annual, long range, subsurface transport of Prorocentrum mariae-lebouriae, from the mouth of the Chesapeake Bay to its bloom area in the upper bay, a distance of 240 km, is described and completely documented. Prorocentrum in surface outflowing waters at the mouth of the bay is recruited in late winter into more dense inflowing coastal waters. Strong stratification produced by late winter--early spring surface runoff results in the development of a stable pycnocline. Prorocentrum, now in northward-flowing bottom waters, is retained in these bottom waters. It accumulates in a subsurface concentration maximum below the pycnocline and is transported northward tomore » reach its bloom area in the Patapsco River and north of the Bay Bridge by late spring. The rapidly decreasing depth of the upper bay causes the pycnocline to rise, mixing the previously light-limited Prorocentrum and its nutrient-rich bottom waters to the surface, where rapid growth ensues. Once the dinoflagellate is in surface waters, positive phototaxis, combined with both wind- and tide-driven surface convergences, produce dense surface patches or red tides. Prorocentrum is effectively retained in the bay until late winter by sequential inoculation into the tributary estuaries on the western shore, which exchange relatively slowly with bay waters. By late winter the annual cycle is complete. Prorocentrum is again in surface waters at the mouth of the bay where it is reintroduced into northward-flowing bottom waters. The mechanisms described provide a key to understanding the origins of subsurface chlorophyll maxima and the delivery of toxic dinoflagellates to coastal bloom areas.« less

Millennial-scale changes of surface and bottom water conditions in the northwestern Pacific during the last deglaciation

NASA Astrophysics Data System (ADS)

Kim, Sunghan; Khim, Boo-Keun; Ikehara, Ken; Itaki, Takuya; Shibahara, Akihiko; Yamamoto, Masanobu

2017-07-01

Changes in water column conditions in the northwestern Pacific during the last 23 ka were reconstructed using geochemical and isotope proxies and redox elemental compositions along with published data (alkenone sea surface temperature (SST) and benthic foraminiferal fauna) at core GH02-1030. Surface water primary productivity in terms of biogenic opal and TOC contents, which mainly represented export production of diatom, was closely related to alkenone (spring-summer) SST and the development of spring-summer mixed layer depth. The different variation patterns of nitrate and silicic acid utilization, estimated by bulk δ15N and δ30Sidiatom values, respectively, are most likely due to the water column denitrification influence on bulk δ15N. Dysoxic bottom water conditions occurred during the Bølling-Allerød (BA) and the Pre-Boreal (PB), which was evident by laminated sediments, abundant dysoxic benthic foraminifers, and increased redox elemental compositions. Although surface water productivity increased during the BA and PB, dysoxic bottom water conditions were caused by a combination of enhanced surface water productivity and reduced ventilation of North Pacific Intermediate Water (NPIW) in response to meltwater input from the high latitude areas. Based on records of core GH02-1030 and other cores in the northwestern Pacific, the Okhotsk Sea, and the Bering Sea, which are all proximal to the modern NPIW source region, dissolved oxygen concentrations of bottom water were more depleted during the BA than PB. Such difference was attributed to more sluggish NPIW ventilation due to more meltwater input during the BA than the PB. The opening or closure of the Bering Strait is critical to the direction of meltwater transport to the northwestern Pacific.

Reynolds Number Effect on Spatial Development of Viscous Flow Induced by Wave Propagation Over Bed Ripples

NASA Astrophysics Data System (ADS)

Dimas, Athanassios A.; Kolokythas, Gerasimos A.

Numerical simulations of the free-surface flow, developing by the propagation of nonlinear water waves over a rippled bottom, are performed assuming that the corresponding flow is two-dimensional, incompressible and viscous. The simulations are based on the numerical solution of the Navier-Stokes equations subject to the fully-nonlinear free-surface boundary conditions and appropriate bottom, inflow and outflow boundary conditions. The equations are properly transformed so that the computational domain becomes time-independent. For the spatial discretization, a hybrid scheme is used where central finite-differences, in the horizontal direction, and a pseudo-spectral approximation method with Chebyshev polynomials, in the vertical direction, are applied. A fractional time-step scheme is used for the temporal discretization. Over the rippled bed, the wave boundary layer thickness increases significantly, in comparison to the one over flat bed, due to flow separation at the ripple crests, which generates alternating circulation regions. The amplitude of the wall shear stress over the ripples increases with increasing ripple height or decreasing Reynolds number, while the corresponding friction force is insensitive to the ripple height change. The amplitude of the form drag forces due to dynamic and hydrostatic pressures increase with increasing ripple height but is insensitive to the Reynolds number change, therefore, the percentage of friction in the total drag force decreases with increasing ripple height or increasing Reynolds number.

Trawling-induced daily sediment resuspension in the flank of a Mediterranean submarine canyon

NASA Astrophysics Data System (ADS)

Martín, Jacobo; Puig, Pere; Palanques, Albert; Ribó, Marta

2014-06-01

Commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution. In particular, trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves, but the issue is at present poorly documented with direct observations. This paper analyses changes in water turbidity in a tributary valley of the La Fonera (=Palamós) submarine canyon, whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m. A string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years, 2010-2011. The second year, an ADCP profiled the currents 80 m above the seafloor. The results illustrate that near-bottom water turbidity at the study site is heavily dominated, both in its magnitude and temporal patterns, by trawling-induced sediment resuspension at the fishing ground. Resuspended sediments are channelised along the tributary in the form of sediment gravity flows, being recorded only during working days and working hours of the trawling fleet. These sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom, reaching suspended sediment concentrations up to 236 mg l-1 close to the seafloor (5 m above bottom). A few hours after the end of daily trawling activities, water turbidity progressively decreases but resuspended particles remain in suspension for several hours, developing bottom and intermediate nepheloid layers that reach background levels ˜2 mg l-1 before trawling activities resume. The presence of these nepheloid layers was recorded in a CTD+turbidimeter transect conducted across the fishing ground a few hours after the end of a working day. These results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near-bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development.

Color Fringes Bordering Black Stripes at the Bottom of a Swimming Pool

ERIC Educational Resources Information Center

Fuster, Gonzalo; Rojas, Roberto; Slüsarenko, Viktor

2016-01-01

We have observed a nice example of chromatic dispersion due to refraction in water, in the form of color fringes bordering the black stripes that exist at the bottom of a swimming pool. Here we give a qualitative description of the phenomenon, explaining the role of the black stripes and the dispersive index of refraction of water.

What caused the decline of China's largest freshwater lake? Attribution analysis on Poyang Lake water level variations in recent years

NASA Astrophysics Data System (ADS)

Ye, Xuchun; Xu, Chong-Yu; Zhang, Qi

2017-04-01

In recent years, dramatic decline of water level of the Poyang Lake, China's largest freshwater lake, has raised wide concerns about the water security and wetland ecosystem. This remarkable hydrological change coincided with several factors like the initial operation of the Three Gorges Dam (TGD) in 2003, the big change of lake bottom topography due to extensive sand mining in the lake since 2000, and also climate change and other human activities in the Yangtze River basin may add to this complexity. Questions raised to what extent that the lake hydrological changes is caused by climate change and/or human activities. In this study, quantitative assessment was conducted to clarify the magnitude and mechanism of specific influencing factors on recent lake decline (2003-2014), with reference to the period of 1980-1999. The attempts were achieved through the reconstruction of lake water level scenarios by the framework of neural network. Major result indicates that the effect of lake bottom topography change due to sand mining activities has became the dominant factor for the recent lake decline, especially in winter season with low water level. However, the effect of TGD regulation shows strong seasonal features, its effect can accounts for 33%-42% of the average water level decline across the lake during the impoundment period of September-October. In addition, the effect of climate change and other human activities over the Yangtze River basin needs to be highly addressed, which is particularly prominent on reducing lake water level during the summer flood season and autumn recession period. The result also revealed that due to different mechanism, the responses of the lake water level to the three influencing factors are not consistent and show great spatial and temporal differences.

Comparison of Water-Load Distributions Obtained during Seaplane Landings with Bureau of Aeronautics Specifications. TED No. NACA 2413

NASA Technical Reports Server (NTRS)

Smiley, Robert F.; Haines, Gilbert A.

1949-01-01

Bureau of Aeronautics Design Specifications SS-IC-2 for water loads in sheltered water are compared with experimental water loads obtained during a full--scale landing investigation. This investigation was conducted with a JRS-1 flying boat which has a 20 degrees dead-rise V-bottom with a partial chine flare. The range of landing conditions included airspeeds between 88 and 126 feet per second, sinking speeds between 1.6 and 9.1 feet per second, flight angles less than 6 degrees, and trims between 2 degrees and 12 degrees. Landings were moderate and were made in calm water. Measurements were obtained of maximum over-all loads, maximum pitching moments, and pressure distributions. Maximum experimental loads include over-all load factors of 2g, moments of 128,000 pound-feet, and maximum local pressures greater than 40 pounds per square inch. Experimental over-all loads are approximately one-half the design values, while local pressures are of the same order as or larger than pressures calculated from specifications for plating, stringer, floor, and frame design. The value of this comparison is limited, to some extent, by the moderate conditions of the test and by the necessary simplifying assumptions used in comparing the specifications with the experimental loads.

Chemical quality of the Saw Mill River, Westchester County, New York, 1981-83

USGS Publications Warehouse

Rogers, R.J.

1984-01-01

Surface waters, bottom sediments and coatings formed on artificial substrates (ceramic tiles) were analyzed to evaluate the chemical quality of the Saw Mill River, New York. Heavy metals, nutrients, and organic contaminants were studied. Dissolved orthophosphate concentrations were highest in the lower third of the river. Dissolved manganese was the only metal to exceed U.S. Environmental Protection Agency water-quality criteria. Arsenic, cadmium, copper, lead, and zinc concentrations were highest in waters from the lowest 4 river miles. Concentrations of copper, lead, and zinc in bottom sediments from the lowest 3 river miles were greater than in upstream sediments. Concentrations of nine heavy metals were higher on tiles emplaced below river mile 3 than on tiles upstream. Few organic compounds were detected in the water column; none persisted at all sites. Chlordane, DDD, DDE, DDT, dieldrin, and polychlorinated biphenyls (PCB's) were found in bottom sediments throughout the basin. PCB concentrations were highest in the lowest 6 river miles; the other organic compounds exhibited no spatial patterns. Polynuclear aromatic hydrocarbons were most abundant in bottom sediments from the lowest 2 river miles. Collectively the distribution of contaminants indicates that river quality deteriorates in the lower, more heavily urbanized reach. (USGS)

Seasonal warming of the Middle Atlantic Bight Cold Pool

NASA Astrophysics Data System (ADS)

Lentz, S. J.

2017-02-01

The Cold Pool is a 20-60 m thick band of cold, near-bottom water that persists from spring to fall over the midshelf and outer shelf of the Middle Atlantic Bight (MAB) and Southern Flank of Georges Bank. The Cold Pool is remnant winter water bounded above by the seasonal thermocline and offshore by warmer slope water. Historical temperature profiles are used to characterize the average annual evolution and spatial structure of the Cold Pool. The Cold Pool gradually warms from spring to summer at a rate of order 1°C month-1. The warming rate is faster in shallower water where the Cold Pool is thinner, consistent with a vertical turbulent heat flux from the thermocline to the Cold Pool. The Cold Pool warming rate also varies along the shelf; it is larger over Georges Bank and smaller in the southern MAB. The mean turbulent diffusivities at the top of the Cold Pool, estimated from the spring to summer mean heat balance, are an order of magnitude larger over Georges Bank than in the southern MAB, consistent with much stronger tidal mixing over Georges Bank than in the southern MAB. The stronger tidal mixing causes the Cold Pool to warm more rapidly over Georges Bank and the eastern New England shelf than in the New York Bight or southern MAB. Consequently, the coldest Cold Pool water is located in the New York Bight from late spring to summer.

Impact of bottom trawling on deep-sea sediment properties along the flanks of a submarine canyon.

PubMed

Martín, Jacobo; Puig, Pere; Masqué, Pere; Palanques, Albert; Sánchez-Gómez, Anabel

2014-01-01

The offshore displacement of commercial bottom trawling has raised concerns about the impact of this destructive fishing practice on the deep seafloor, which is in general characterized by lower resilience than shallow water regions. This study focuses on the flanks of La Fonera (or Palamós) submarine canyon in the Northwestern Mediterranean, where an intensive bottom trawl fishery has been active during several decades in the 400-800 m depth range. To explore the degree of alteration of surface sediments (0-50 cm depth) caused by this industrial activity, fishing grounds and control (untrawled) sites were sampled along the canyon flanks with an interface multicorer. Sediment cores were analyzed to obtain vertical profiles of sediment grain-size, dry bulk density, organic carbon content and concentration of the radionuclide 210Pb. At control sites, surface sediments presented sedimentological characteristics typical of slope depositional systems, including a topmost unit of unconsolidated and bioturbated material overlying sediments progressively compacted with depth, with consistently high 210Pb inventories and exponential decaying profiles of 210Pb concentrations. Sediment accumulation rates at these untrawled sites ranged from 0.3 to 1.0 cm y-1. Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears. Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites. This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea.

Impact of Bottom Trawling on Deep-Sea Sediment Properties along the Flanks of a Submarine Canyon

PubMed Central

Martín, Jacobo; Puig, Pere; Masqué, Pere; Palanques, Albert; Sánchez-Gómez, Anabel

2014-01-01

The offshore displacement of commercial bottom trawling has raised concerns about the impact of this destructive fishing practice on the deep seafloor, which is in general characterized by lower resilience than shallow water regions. This study focuses on the flanks of La Fonera (or Palamós) submarine canyon in the Northwestern Mediterranean, where an intensive bottom trawl fishery has been active during several decades in the 400–800 m depth range. To explore the degree of alteration of surface sediments (0–50 cm depth) caused by this industrial activity, fishing grounds and control (untrawled) sites were sampled along the canyon flanks with an interface multicorer. Sediment cores were analyzed to obtain vertical profiles of sediment grain-size, dry bulk density, organic carbon content and concentration of the radionuclide 210Pb. At control sites, surface sediments presented sedimentological characteristics typical of slope depositional systems, including a topmost unit of unconsolidated and bioturbated material overlying sediments progressively compacted with depth, with consistently high 210Pb inventories and exponential decaying profiles of 210Pb concentrations. Sediment accumulation rates at these untrawled sites ranged from 0.3 to 1.0 cm y−1. Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears. Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites. This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea. PMID:25111298

Mercury distribution in Douro estuary (Portugal).

PubMed

Ramalhosa, E; Pereira, E; Vale, C; Válega, M; Monterroso, P; Duarte, A C

2005-11-01

Determinations of dissolved reactive and total dissolved mercury, particulate and sedimentary mercury, dissolved organic carbon (DOC), particulate organic carbon (POC) and suspended particulate matter (SPM) have been made in the estuary of river Douro, in northern Portugal. The estuary was stratified by salinity along most of its length, it had low concentrations of SPM, typically <20 mg dm(-3), and concentrations of DOC in the range <1.0-1.8 mg dm(-3). The surface waters had a maximum dissolved concentration of reactive mercury of about 10 ng dm(-3), whereas for the more saline bottom waters it was about 65 ng dm(-3). The surface waters had maximum concentrations of total suspended particulate mercury of approximately 7 microg g(-1) and the bottom waters were always <1 microg g(-1). Concentrations of mercury in sediments was low and in the range from 0.06 to 0.18 microg g(-1). The transport of mercury in surface waters was mainly associated with organic-rich particulate matter, while in bottom waters the dissolved phase transport of mercury is more important. Lower particulate organic matter, formation of chlorocomplexes in more saline waters and eventually the presence of colloids appear to explain the difference of mercury partitioning in Douro estuarine waters.

The impact of sedimentary coatings on the diagenetic Nd flux

NASA Astrophysics Data System (ADS)

Abbott, April N.; Haley, Brian A.; McManus, James

2016-09-01

Because ocean circulation impacts global heat transport, understanding the relationship between deep ocean circulation and climate is important for predicting the ocean's role in climate change. A common approach to reconstruct ocean circulation patterns employs the neodymium isotope compositions of authigenic phases recovered from marine sediments. In this approach, mild chemical extractions of these phases is thought to yield information regarding the εNd of the bottom waters that are in contact with the underlying sediment package. However, recent pore fluid studies present evidence for neodymium cycling within the upper portions of the marine sediment package that drives a significant benthic flux of neodymium to the ocean. This internal sedimentary cycling has the potential to obfuscate any relationship between the neodymium signature recovered from the authigenic coating and the overlying neodymium signature of the seawater. For this manuscript, we present sedimentary leach results from three sites on the Oregon margin in the northeast Pacific Ocean. Our goal is to examine the potential mechanisms controlling the exchange of Nd between the sedimentary package and the overlying water column, as well as the relationship between the εNd composition of authigenic sedimentary coatings and that of the pore fluid. In our comparison of the neodymium concentrations and isotope compositions from the total sediment, sediment leachates, and pore fluid we find that the leachable components account for about half of the total solid-phase Nd, therefore representing a significant reservoir of reactive Nd within the sediment package. Based on these and other data, we propose that sediment diagenesis determines the εNd of the pore fluid, which in turn controls the εNd of the bottom water. Consistent with this notion, despite having 1 to 2 orders of magnitude greater Nd concentration than the bottom water, the pore fluid is still <0.001% of the total Nd reservoir in the upper sediment column. Therefore, the pore fluid reservoir is too small to maintain a unique signature, and instead must be controlled by the larger reservoir of Nd in the reactive coatings. In addition, to achieve mass balance, we find it necessary to invoke a cryptic radiogenic (εNd of +10) trace mineral source of neodymium within the upper sediment column at our sites. When present, this cryptic trace metal results in more radiogenic pore fluid.

Optimization and evaluation of a bottom substrate denitrification tank for nitrate removal from a recirculating aquaculture system.

PubMed

Pungrasmi, Wiboonluk; Playchoom, Cholticha; Powtongsook, Sorawit

2013-08-01

A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank (0.04 m2 tank surface area), packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions (e.g. > 2 mg/L) while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested (soil, sand, pumice stone and vermiculite), pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD:N ratio of 5:1, a nitrate removal rate of 4591 +/- 133 mg-N/m2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD:N ratio of 5:1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 +/- 945 mg-N/m2 tank bottom area/day or 126 +/- 18 mg-N/L of pumice packing volume/day.

Suspended Alexandrium spp. hypnozygote cysts in the Gulf of Maine

NASA Astrophysics Data System (ADS)

Kirn, Sarah L.; Townsend, David W.; Pettigrew, Neal R.

2005-09-01

The life cycle of dinoflagellates of the genus Alexandrium includes sexual reproduction followed by the formation of a dormant hypnozygote cyst, which serves as a resting stage. Negatively buoyant cysts purportedly fall to the benthos where they undergo a mandatory period of quiescence. Previous reports of cysts in the surficial sediments of the Gulf of Maine, where Alexandrium blooms are well documented, show a broad distribution of cysts, with highest concentrations generally in sediments below 100 m depth. We report here an exploration of cysts suspended in the water column, where they would be better positioned to inoculate springtime Alexandrium populations. During cruises in February, April, and June of 2000, water samples were collected at depths just off the bottom (within 5 m), at the top of the bottom nepheloid layer, and near the surface (1 m) and examined for cyst concentrations. Suspended cysts were found throughout the Gulf of Maine and westernmost Bay of Fundy. Planktonic cyst densities were generally greater in near-bottom and top of the bottom nepheloid layer samples than in near-surface water samples; densities were of the order of 10 2 cysts m -3 in surface waters, and 10 2-10 3 cysts m -3 at near-bottom depths. Temporally, they were most abundant in February and least abundant in April. Reports by earlier workers of cysts in the underlying sediments were on the order of 10 3 cysts cm -3. We present calculations that demonstrate the likelihood of cyst resuspension from bottom sediments forced by swell and tidal currents, and propose that such resuspended cysts are important in inoculating the seasonal bloom. We estimate that suspended cysts may contribute significantly to the annual vegetative cell population in the Gulf of Maine.

Natural and artificial radionuclides in the Suez Canal bottom sediments and stream water

NASA Astrophysics Data System (ADS)

El-Tahawy, M. S.; Farouk, M. A.; Ibrahiem, N. M.; El-Mongey, S. A. M.

1994-07-01

Concentration of natural and artificial radionuclides in Suez Canal bottom sediments and stream water have been measured using γ spectrometers based on a hyper-pure Ge detector. The activity concentrations of 238U series, 232Th series and 40K did not exceed 16.0, 15.5 and 500.0 Bq kg-1 dry weight for sediments. The activity concentration of 238U series and 40K did not exceed 0.6 and 18.0 Bq 1-1 for stream water.

Impulse Loading Resulting fromShallow Buried Explosives in Water-Saturated Sand

DTIC Science & Technology

2007-01-01

speed photographs of the associated soil cratering and ejecting phenomena. The work of Bergeron et al. [6] was subsequently extended by Braid [7] to...place, a series of water hoses is placed in pit bottom to allow the introduction of water into the pit from the bottom. Next, approximately 14.2 m3...blast. Final report for contract no. DAAK70-92-C-0058, US Army Belvoir RDEC, Ft. Belvoir, VA, 1993. 6 Bergeron, D. Hlady, S., and Braid , M. P

Flows of bottom water in fractures of the North Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Morozov, E. G.; Tarakanov, R. Yu.; Demidova, T. A.; Makarenko, N. I.

2017-06-01

It has been shown that the total transport of Antarctic Bottom Water (AABW) in the northern fractures (Kane, Cabo Verde, Marathon) are one order of magnitude smaller than in the southern fractures (Vema, Doldrums, Vernadsky). The estimates of AABW transport through this group of fractures based on measurements in 2014 were approximately 0.28 Sv, which is about 25% of the transport through the Vema Fracture Zone. However, the coldest water flows through the Vema Fracture Zone.

Detection to the DepositFan Occurring in the Sun Moon Lake Using Geophysical Sonar Data

NASA Astrophysics Data System (ADS)

Mimi, L.

2014-12-01

Located in central Taiwan, the Sun Moon Lake is an U-shaped basin with the waters capacity for 138.68 × 106m³. The water is input through two underground tunnels from the Wu-Jie dam in the upstream of the Zhuo-shui river. Although the Wu-Jie dam has been trying to keep the tunnels transporting clean water into the lake, the water is still mixed with muds. The silty water brings the deposits accumulating outwards from positions of the tunnel outlets resulting in a deposit fan formed in the lake. To monitor how the fan is accumulated is then very important in terms of environmental issue, tourism and electric power resources. Institute of Oceanography, National Taiwan University therefore conducted projects to use the multi-beam echo sounders to collect bathymetric data, and used the Chirp sub-bottom profiler to explore silted pattern inside the deposit fan. With these data, underwater topographic maps were plotted to observe the shape and internal structure of the fan. Moreover, two sets of data obtained in 2006 and 2012 were used to estimate the siltation magnitude and pattern in the six years period.The multi-beam sounder is Resons Seabat 9001s model; it collects 60 values in each of the swaths positioned by the DGPS method.The sub-bottom profiler is the EdgeTech 3100P Chirp Sonar, its acoustic wave frequency is in 2 ~ 16kHz. The data give the siltation amount in the Sun Moon Lake was around 3× 106 m³, which gives annual siltation rate at 5× 105 m³. The leading edge of the deposit fan has been expanded westwards 2 km from the water outlet since the tunnel was built 70 years ago; however, outside the deposit fan, the siltation shows insignificant amount on the water bottom.In the past few years the siltation mainly occurs outside in the east side of lake, more closer to the water outlets, the terrain had been increased from 744 m to 746 m (748.5 meters is stranded level of the lake).Observing sub-bottom profiler data, we can clearly see the location of the paleo-hard- bottom of the lake before the siltation occurred. These sub-bottom profiles can be used to check or to analyze episodic deposition behavior in producing the deposit fan.

Clay minerals in sediments of Portuguese reservoirs and their significance as weathering products from over-eroded soils: a comparative study of the Maranhão, Monte Novo and Divor Reservoirs (South Portugal)

NASA Astrophysics Data System (ADS)

Fonseca, Rita M. F.; Barriga, Fernando J. A. S.; Conceição, Patrícia I. S. T.

2010-12-01

The Southern region of Portugal is subjected to several forms of over-erosion. Most leached products, mainly composed of fine particles containing nutrients, metals or pesticides, are easily transported by river flows. When these are hindered by a physical barrier such as a dam, the particulate load accumulates on the bottom of the reservoirs, often leading to a pronounced decrease of water quality. Bottom sediments from three reservoirs were subjected to grain-size analysis and a study of clay minerals by X-ray diffraction. Most sediments contain a diverse set of clay minerals, mostly illites, smectites, chlorites and kaolinites. The nature of the clay minerals reflects the nature of the parent rocks. During the cycles of transport and temporary deposition, they may undergo significant chemical and physical transformations, which lead to an increase of expandable properties and therefore, to a higher cationic exchange capacity, determining its important role as vehicles of environmental pollutants.

Sensitivity of Hypoxia Predictions for the Northern Gulf of Mexico to Sediment Oxygen Consumption and Model Nesting

NASA Astrophysics Data System (ADS)

Fennel, Katja; Hu, Jiatang; Laurent, Arnaud; Marta-Almeida, Martinho; Hetland, Robert

2014-05-01

Interannual variations of the hypoxic area that develops every summer over the Texas-Louisiana Shelf are large. The 2008 Action Plan put forth by an alliance of multiple state and federal agencies and tribes calls for a decrease of the hypoxic area through nutrient management in the watershed. Realistic models help build mechanistic understanding of the processes underlying hypoxia formation and are thus indispensable for devising efficient nutrient reduction strategies. Here we present such a model, evaluate its hypoxia predictions against monitoring observations and assess the sensitivity of hypoxia predictions to model resolution, variations in sediment oxygen consumption and choice of physical horizontal boundary conditions. We find that hypoxia predictions on the shelf are very sensitive to the parameterization of sediment oxygen consumption, a result of the fact that hypoxic conditions are restricted to a relatively thin layer above the bottom over most of the shelf. We also show that the strength of vertical stratification is an important predictor of oxygen concentration in bottom waters and that modification of physical horizontal boundary conditions can have a large effect on hypoxia predictions.

Modeling the formation of the quench product in municipal solid waste incineration (MSWI) bottom ash.

PubMed

Inkaew, Kanawut; Saffarzadeh, Amirhomayoun; Shimaoka, Takayuki

2016-06-01

This study investigated changes in bottom ash morphology and mineralogy under lab-scale quenching conditions. The main purpose was to clarify the mechanisms behind the formation of the quench product/layer around bottom ash particles. In the experiments, the unquenched bottom ashes were heated to 300°C for 1h, and were quenched by warm water (65°C) with different simulated conditions. After having filtered and dried, the ashes were analyzed by a combination of methodologies namely, particle size distribution analysis, intact particle and thin-section observation, X-ray diffractometry, and scanning electron microscope with energy dispersive X-ray spectroscopy. The results indicated that after quenching, the morphology and mineralogy of the bottom ash changed significantly. The freshly quenched bottom ash was dominated by a quench product that was characterized by amorphous and microcrystalline calcium-silicate-hydrate (CSH) phases. This product also enclosed tiny minerals, glasses, ceramics, metals, and organic materials. The dominant mineral phases produced by quenching process and detected by XRD were calcite, Friedel's salt, hydrocalumite and portlandite. The formation of quench product was controlled by the fine fraction of the bottom ash (particle size <0.425mm). From the observations, a conceptual model of the ash-water reactions and formation of the quench product in the bottom ash was proposed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Field measurements of the spectral response of natural waters

NASA Technical Reports Server (NTRS)

Bartolucci, L. A.; Robinson, B. F.; Silva, L. F.

1977-01-01

The spectral response (air-water interface reflectance and water-volume scattering) of turbid river water (99 mg/liter suspended solids) and relatively clear lake water (10 mg/liter suspended solids) was measured in situ with a field spectroradiometer. The influence of the river bottom on the spectral response of the water also was determined by using a modified Secchi disc approach. The results indicated that turbid river water had a higher spectral response than clear lake water (about 6 percent) in the red (0.6-0.7 micron) and near-infrared (0.7-0.9 micron) portions of the spectrum. Also, the reflectance characteristics of the river bottom did not influence the spectral response of the turbid river water when the water was deeper than 30 cm

An analytical model for subsurface irradiance and remote sensing reflectance in deep and shallow case-2 waters.

PubMed

Albert, A; Mobley, C

2003-11-03

Subsurface remote sensing signals, represented by the irradiance re fl ectance and the remote sensing re fl ectance, were investigated. The present study is based on simulations with the radiative transfer program Hydrolight using optical properties of Lake Constance (German: Bodensee) based on in-situ measurements of the water constituents and the bottom characteristics. Analytical equations are derived for the irradiance re fl ectance and remote sensing re fl ectance for deep and shallow water applications. The input of the parameterization are the inherent optical properties of the water - absorption a(lambda) and backscattering bb(lambda). Additionally, the solar zenith angle thetas, the viewing angle thetav , and the surface wind speed u are considered. For shallow water applications the bottom albedo RB and the bottom depth zB are included into the parameterizations. The result is a complete set of analytical equations for the remote sensing signals R and Rrs in deep and shallow waters with an accuracy better than 4%. In addition, parameterizations of apparent optical properties were derived for the upward and downward diffuse attenuation coefficients Ku and Kd.

Hysteretic growth and decay of a waterspout column

NASA Astrophysics Data System (ADS)

Naumov, Igor V.; Herrada, Miguel A.; Sharifullin, Bulat R.; Shtern, Vladimir N.

2018-02-01

This work explores a model waterspout: a flow of water and sunflower oil driven by the rotating lid in a sealed vertical cylindrical container. The experiments reveal the hysteretic growth and decay of a water column. The numerical simulations uncover vortex breakdown (VB) in the water and oil flows. As the rotation speeds up, (1) a VB water cell emerges near the bottom center, (2) it expands and occupies almost the entire water volume except a thin layer adjusted to the interface, (3) a VB oil cell emerges and disappears above the interface-axis intersection, (4) the interface rises near the axis, descends at the periphery, and shifts from the sidewall to the bottom, (5) the water touches the lid near the axis and forms a column, extending from the bottom up to the lid. As the rotation decelerates, the process reverses, but the flow states differ from those for the direct process at same rotation speeds. It is argued that the hysteresis is a capillary phenomenon and occurs because the interface-wall contact angle differs in the direct and reverse processes.

Surface-geophysical characterization of ground-water systems of the Caloosahatchee River basin, southern Florida

USGS Publications Warehouse

Cunningham, Kevin J.; Locker, Stanley D.; Hine, Albert C.; Bukry, David; Barron, John A.; Guertin, Laura A.

2001-01-01

The Caloosahatchee River Basin, located in southwestern Florida, includes about 1,200 square miles of land. The Caloosahatchee River receives water from Lake Okeechobee, runoff from the watershed, and seepage from the underlying ground-water systems; the river loses water through drainage to the Gulf of Mexico and withdrawals for public-water supply and agricultural and natural needs. Water-use demands in the Caloosahatchee River Basin have increased dramatically, and the Caloosahatchee could be further stressed if river water is used to accommodate restoration of the Everglades. Water managers and planners need to know how much water will be used within the river basin and how much water is contributed by Lake Okeechobee, runoff, and ground water. In this study, marine seismic-reflection and ground-penetrating radar techniques were used as a means to evaluate the potential for flow between the river and ground-water systems. Seven test coreholes were drilled to calibrate lithostratigraphic units, their stratal geometries, and estimated hydraulic conductivities to surface-geophysical profiles. A continuous marine seismic-reflection survey was conducted over the entire length of the Caloosahatchee River and extending into San Carlos Bay. Lithostratigraphic units that intersect the river bottom and their characteristic stratal geometries were identified. Results show that subhorizontal reflections assigned to the Tamiami Formation intersect the river bottom between Moore Haven and about 9 miles westward. Oblique and sigmoidal progradational reflections assigned to the upper Peace River Formation probably crop out at the floor of the river in the Ortona area between the western side of Lake Hicpochee and La Belle. These reflections image a regional-scale progradational deltaic depositional system containing quartz sands with low to moderate estimated hydraulic conductivities. In an approximate 6-mile length of the river between La Belle and Franklin Lock, deeper karstic collapse structures are postulated. These structures influence the geometries of parallel reflections that intersect the river channel. Here, reflections assigned to the Buckingham Limestone Member of the Tamiami Formation (a confining unit) and reflections assigned to the clastic zone of the sandstone aquifer likely crop out at the river bottom. Beneath these shallow reflections, relatively higher amplitude parallel reflections of the carbonate zone of the sandstone aquifer are well displayed in the seismic-reflection profiles. In San Carlos Bay, oblique progradational reflections assigned to the upper Peace River Formation are shown beneath the bay. Almost everywhere beneath the river, a diffuse ground-water flow system is in contact with the channel bottom. Ground-penetrating radar profiles of an area about 2 miles north of the depositional axis of the deltaic depositional system in the Ortona area show that progradational clinoforms imaged on seismic reflection profiles in the Caloosahatchee River are present within about 17 feet of the ground surface. Ground-penetrating radar profiles show southward dipping, oblique progradational reflections assigned to the upper Peace River Formation that are terminated at their tops by a toplapping or erosional discontinuity. These clinoformal reflections image clean quartz sand that is probably characterized by moderate hydraulic conductivity. This sand could be mapped using ground-penetrating radar methods.

Quality of water in Luxapallia Creek at Columbus, Mississippi

USGS Publications Warehouse

Kalkhoff, Stephen J.

1982-01-01

The results of a water quality study of a short reach of Luxapallila Creek at Columbus, Mississippi, during September 9-12, 1979, indicate that the water is colored (60 units) and has a low dissolved solids content (44 mg/L). The dissolved oxygen concentration, temperature, and pH of the water in Luxapallila Creek changed a slightly downstream through the study reach. The mean specific conductance almost doubled and the five-day biochemical oxygen demand load increased over four times through the study reach. The fecal coliform to fecal streptococcus ration of 3 to 5 samples collected at the downstream site was greater than 4.0, strongly suggesting the presence of human waste. The concentrations of iron and manganese at the downstream site exceeded the U.S. Environmental Protection Agency 's criteria for domestic water supplies. High concentrations of iron, manganese, and lead also were present in a bottom material sample at the downstream site. (USGS)

Model testing of radioactive contamination by 90Sr, 137Cs and 239,240Pu of water and bottom sediments in the Techa River (Southern Urals, Russia).

PubMed

Kryshev, I I; Boyer, P; Monte, L; Brittain, J E; Dzyuba, N N; Krylov, A L; Kryshev, A I; Nosov, A V; Sanina, K D; Zheleznyak, M I

2009-03-15

This paper presents results of testing models for the radioactive contamination of river water and bottom sediments by (90)Sr, (137)Cs and (239,240)Pu. The scenario for the model testing was based on data from the Techa River (Southern Urals, Russia), which was contaminated as a result of discharges of liquid radioactive waste into the river. The endpoints of the scenario were model predictions of the activity concentrations of (90)Sr, (137)Cs and (239,240)Pu in water and bottom sediments along the Techa River in 1996. Calculations for the Techa scenario were performed by six participant teams from France (model CASTEAUR), Italy (model MARTE), Russia (models TRANSFER-2, CASSANDRA, GIDRO-W) and Ukraine (model RIVTOX), all using different models. As a whole, the radionuclide predictions for (90)Sr in water for all considered models, (137)Cs for MARTE and TRANSFER-2, and (239,240)Pu for TRANSFER-2 and CASSANDRA can be considered sufficiently reliable, whereas the prediction for sediments should be considered cautiously. At the same time the CASTEAUR and RIVTOX models estimate the activity concentrations of (137)Cs and (239,240)Pu in water more reliably than in bottom sediments. The models MARTE ((239,240)Pu) and CASSANDRA ((137)Cs) evaluated the activity concentrations of radionuclides in sediments with about the same agreement with observations as for water. For (90)Sr and (137)Cs the agreement between empirical data and model predictions was good, but not for all the observations of (239,240)Pu in the river water-bottom sediment system. The modelling of (239,240)Pu distribution proved difficult because, in contrast to (137)Cs and (90)Sr, most of models have not been previously tested or validated for plutonium.

Measurements of slope currents and internal tides on the Continental Shelf and slope off Newport Beach, California

USGS Publications Warehouse

Rosenberger, Kurt J.; Noble, Marlene A.; Norris, Benjamin

2014-01-01

An array of seven moorings housing current meters and oceanographic sensors was deployed for 6 months at 5 sites on the Continental Shelf and slope off Newport Beach, California, from July 2011 to January 2012. Full water-column profiles of currents were acquired at all five sites, and a profile of water-column temperature was also acquired at two of the five sites for the duration of the deployment. In conjunction with this deployment, the Orange County Sanitation District deployed four bottom platforms with current meters on the San Pedro Shelf, and these meters provided water-column profiles of currents. The data from this program will provide the basis for an investigation of the interaction between the deep water flow over the slope and the internal tide on the Continental Shelf.

A novel method for determination of aragonite saturation state on the continental shelf of central Oregon using multi-parameter relationships with hydrographic data

NASA Astrophysics Data System (ADS)

Juranek, L. W.; Feely, R. A.; Peterson, W. T.; Alin, S. R.; Hales, B.; Lee, K.; Sabine, C. L.; Peterson, J.

2009-12-01

We developed a multiple linear regression model to robustly determine aragonite saturation state (Ωarag) from observations of temperature and oxygen (R2 = 0.987, RMS error 0.053), using data collected in the Pacific Northwest region in late May 2007. The seasonal evolution of Ωarag near central Oregon was evaluated by applying the regression model to a monthly (winter)/bi-weekly (summer) water-column hydrographic time-series collected over the shelf and slope in 2007. The Ωarag predicted by the regression model was less than 1, the thermodynamic calcification/dissolution threshold, over shelf/slope bottom waters throughout the entire 2007 upwelling season (May-November), with the Ωarag = 1 horizon shoaling to 30 m by late summer. The persistence of water with Ωarag < 1 on the continental shelf has not been previously noted and could have notable ecological consequences for benthic and pelagic calcifying organisms such as mussels, oysters, abalone, echinoderms, and pteropods.

Predation by dipteran larvae on fairy shrimp (Crustacea: Anostraca) in Utah rock pools

USGS Publications Warehouse

Graham, T.B.

1994-01-01

A series of experiments examined how ecological factors affect notonectid foraging success on fairy shrimp. Variation in pond depth over natural ranges had no direct effect on notonectid ability to capture fairy shrimp. Decreases in water clarity over natural ranges led to decreased notonectid ability to capture fairy shrimp. This corresponds with the observation that six weeks after the fairy shrimp hatched they were more likely to be present in cloudy ponds than in ponds containing clearer water. If correct, this is a situation where physical factors have a major effect on how a biological interaction influences the local distribution of species. It appears water depth indirectly affects notonectid foraging rates, as shallow ponds are apparently made cloudy by wind-driven waves disturbing the bottom mud. These results suggest the notonectid-fairy shrimp interaction will not be a constant for any given pond, but will depend on abiotic factors like amount of rainfall and frequency of windy conditions.

Long-term observations of bottom conditions and sediment movement on the Atlantic continental shelf; time-lapse photography from instrumented tripod

USGS Publications Warehouse

Butman, Bradford; Bryden, Cynthia G.; Pfirman, Stephanie L.; Strahle, William J.; Noble, Marlene A.

1984-01-01

An instrument system that measures bottom current, temperature, light transmission, and pressure, and that photographs the bottom at 2- to 6-hour intervals has been developed to study sediment transport on the Atlantic Continental Shelf. Instruments have been deployed extensively along the United States East Coast Continental Shelf for periods of from 2 to 6 months to study the frequency, direction, and rate of bottom sediment movement, and the processes causing movement. The time-lapse photographs are used to (1) characterize the bottom benthic community and surface microtopography; (2) monitor changes in the bottom topography and near-bottom water column caused by currents and storms (for example, ripple generation and migration, sediment resuspension); and (3) monitor seasonal changes in the bottom benthic community and qualitative effects of this community on the bottom sediments.

Water conditions and geochemistry in northern Adriatic anoxia-prone areas and response of benthic faunas to oxygen deficiencies

NASA Astrophysics Data System (ADS)

Zuschin, Martin; Riedel, Bettina; Stachowitsch, Michael; Cermelj, Branko

2010-05-01

One predicted effect of global climate change, specifically global warming, is the increase in the temperatures and stratification of shallow coastal and estuarine systems. This, coupled with ongoing anthropogenic eutrophication, will exacerbate hypoxia and benthic mortalities, significantly damaging these critical marine ecosystems. These phenomena are particularly severe on sublitoral soft-bottoms such as the poorly sorted silty sands at the study site in the northern Adriatic Sea. We deployed a specially developed underwater chamber to artificially induce anoxia in situ. Our Experimental Anoxia Generating Unit (EAGU) is a large plexiglass chamber that combines a digital camera with oxygen/hydrogen sulphide/pH sensors along with flashes and battery packs. The unit can be deployed for up to five days to autonomously generate oxygen crises and quantify both physico-chemical parameters and benthic responses. The system is initially positioned in an "open" configuration (open-sided aluminium frame) over the benthic fauna ("control" experiment). After 24 h the EAGU is switched to its "closed" configuration (plexiglass enclosure) and repositioned over the same assemblage. In this contribution, we focus on the natural oxygen content, temperature and pH of bottom waters during summer, the course of oxygen decrease during our experiments and the onset of H2S development. Oxygen content of the bottom water, a few centimetres above the sediment-water interface, ranges from ~3.5-8 but is mostly between 4-6 ml l-1 during July to September of the study periods (2005 and 2006) and decreases to zero within ~1-3 days after initiation of our experiments. In parallel, H2S starts to develop at the onset of anoxia. Water temperatures at the bottom were stable during experiments and ranged from 18.5°C to 21.4°C, but pH decreased from 8.3 to 8.1 at the beginning to 7.9 to 7.7 at the end of the experiments. Sediment profiling indicates that the diffusive benthic boundary layer is approximately 2.5 mm thick and that oxygen values decrease from ~2 ml l-1 3.5 mm above the sediment water interface to virtually zero at the interface. PH-values in 2 mm depth decrease from 8.15 to 7.6 within the first 10 h of the experiment. This indicates that the most reactive organic matter is decomposing in the uppermost few mm of the sediment. These data can be related to behavioural responses and mortality sequences of benthic faunas, including echinoids, crustaceans, molluscs and anemones. Beginning hypoxia (≤2.0 ml l-1 DO) elicited escape patterns such as increased horizontal and vertical locomotion of animals. Moderate hypoxia (≤1.0 ml l-1 DO) triggered species-specific sublethal effects such as arm-tipping in ophiuroids or extension from the sediment in sea anemones. At severe hypoxia (≤0.5 ml l-1 DO) infaunal organisms began to emerge and first mortalities occurred. Some crustaceans and echinoderms are among the first to die, but sea anemones and large gastropods can even survive the onset of hydrogen sulfide.

A 1000-year sediment record of recurring hypoxia off the Mississippi River: The potential role of terrestrially-derived organic matter inputs

USGS Publications Warehouse

Swarzenski, P.W.; Campbell, P.L.; Osterman, L.E.; Poore, R.Z.

2008-01-01

A suite of inorganic and organic geochemical tracers and a low-oxygen tolerant benthic faunal index ('PEB') were measured in a 14C-dated 2+??m long gravity core collected on the Louisiana shelf adjacent to the Mississippi River delta to study potential millennium-scale low-oxygen events. Periodic down-core excursions in the PEB index throughout the core suggest recurring, natural bottom water low-oxygen events that extend back ??? 1000??14C years. Select trace element and biomarker distributions in these same sediments were examined as potential tracers of past hypoxic events and to help distinguish between marine versus terrestrial processes involved in organic carbon production. In discrete sediment horizons where the PEB index was elevated, redox-sensitive vanadium concentrations were consistently depleted, excursions in sedimentary ??13C suggest periodic, preferential terrestrial inputs, and the concentrations of two sterol biomarkers (sitosterol and ??-stigmasterol) also showed concurrent enrichments. If the PEB index successfully records ??? 1000??14C year-scale low-oxygen events, then the distribution of these geochemical tracers can be interpreted to corroborate the view that naturally occurring low-oxygen bottom water conditions have existed on the inner Louisiana continental shelf, not only in recent times, but also over at least the last 1000??14C years. These data support the general hypothesis that historic, low-oxygen bottom water conditions on the Louisiana shelf are likely tied to periods of increased fluvial discharge and associated wetland export in the absence of modern river levees. Enhanced river discharge and associated material export would both stimulate enhanced in situ organic carbon production and foster water column stratification. Such periodic elevated river flows during the last millennium can be linked to climate fluctuations and tropical storm activity. ?? 2008 Elsevier B.V. All rights reserved.

Observations of Antarctic Slope Current Transport and Dense Water Flow in the Northwestern Weddell Sea

NASA Astrophysics Data System (ADS)

Azaneu, M. V. C.; Heywood, K. J.; Queste, B. Y.; Thompson, A. F.

2016-02-01

In early 2012 the GENTOO project deployed three Seagliders in the northwest Weddell Sea, acquiring high temporal and spatial resolution measurements around Powell Basin for a period of 10 weeks. The Antarctic Slope Front and associated currents form a physical and dynamical barrier to the cross-slope exchange of properties, influencing local and global ocean dynamics. The Seaglider dataset comprises 1598 temperature and salinity profiles and is used to better understand cross-slope processes. From this dataset, 582 glider profiles with altimetric information at the east Antarctic Peninsula continental slope are used to investigate the properties and thickness of the dense bottom water spilling off the shelf. The dense water is identified mostly over the slope, between the 500 and 1000 m isobaths. The dense layer is thickest around ˜ 63.33 °S, along the 1000 m isobath, becoming thinner onshore and towards northern areas. We also evaluate with unprecedented resolution the along-stream velocity and potential vorticity fields along the 17 transects across the eastern Antarctic Peninsula shelf-break and the 4 transects that cross the South Orkney Islands plateau. Using an improved hydrodynamic flight model, we reference the geostrophic shear to the glider-derived depth-averaged currents corrected for tides. In the western Weddell Sea, the geostrophic velocities fields indicate the presence of a surprisingly weakened Antarctic Slope Current (ASC) around 63.5 °S, possibly indicative of high eddy activity in the area. ASC transport in this southernmost section is less than 0.2 Sv. In a more northerly section (˜ 63.1 °S), the ASC transport reaches 6 Sv. The transects west of the South Orkney Island indicate a northward flow, opposite to the previously assumed regime. The results also show intensified northward bottom flows close to the slope, which can be related to processes occurring in the bottom boundary layer. The potential vorticity fields are used to identify potential instability mechanisms contributing to the cross-slope exchange of water mass properties.

On the formation of glide-snow avalanches

NASA Astrophysics Data System (ADS)

Mitterer, C.; Schweizer, J.

2012-12-01

On steep slopes the full snowpack can glide on the ground; tension cracks may open and eventually the slope may fail as a glide-snow avalanche. Due to their large mass they have considerable destructive potential. Glide-snow avalanches typically occur when the snow-soil interface is moist or wet so that basal friction is reduced. The occurrence, however, of glide cracks and their evolution to glide avalanches are still poorly understood. Consequently, glides are difficult to predict as (i) not all cracks develop into an avalanche, and (ii) for those that do, the time between crack opening and avalanche event might vary from hours to weeks - or on the other hand be so short that there is no warning at all by crack opening. To improve our understanding we monitored several slopes and related glide snow activity to meteorological data. In addition, we explored conditions that favor the formation of a thin wet basal snowpack layer with a physical-based model representing water and heat flux at the snow-soil interface. The statistical analyses revealed that glide-snow avalanche activity might be associated to an early season and a spring condition. While early season conditions tend to have warm and dry autumns followed by heavy snowfalls, spring conditions showed good agreement with increasing air temperature. The model indicates that energy (summer heat) stored in the ground might be sufficient to melt snow at the bottom of the snowpack. Due to capillary forces, water will rise for a few centimeters into the snowpack and thereby reduce friction at the interface. Alternatively, we demonstrate that also in the absence of melt water production at the bottom of the snowpack water may accumulate in the bottom layer due to an upward flux into the snowpack if a dry snowpack overlies a wet soil. The particular conditions that are obviously required at the snow-soil interface explain the strong winter-to-winter variations in snow gliding.

Global Compilation of Marine Varve Records

NASA Astrophysics Data System (ADS)

Schimmelmann, A.; Lange, C.; Schieber, J.; Francus, P.; Ojala, A.; Zolitschka, B.

2016-02-01

Marine varves contain highly resolved records of geochemical and other paleoceanographic and paleoenvironmental proxies with annual to seasonal resolution. We present a global compilation of marine varved sedimentary records throughout the Holocene and Quaternary covering more than 50 sites worldwide. Marine varve deposition and preservation typically depend on environmental and sedimentological principles, such as a sufficiently high sedimentation rate, severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos, and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern. Additional oceanographic factors may include the strength and depth range of the Oxygen Minimum Zone (OMZ) and regional anthropogenic eutrophication. Modern to Quaternary marine varves are not only found in those parts of the open ocean that comply with these principles, but also in fjords, embayments and estuaries with thermohaline density stratification, and nearshore `saline lakes' with strong hydrologic connections to ocean water. Marine varves have also been postulated in pre-Quaternary rocks. In the case of non-evaporitic laminations in fine-grained ancient marine rocks, laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transported and sorted silt-sized particles, clay floccules, and organic-mineral aggregates in the form of migrating bedload ripples. Modern marine ecosystems on continental shelves and slopes, in coastal zones and in estuaries are susceptible to stress by various factors that may result in oxygen-depletion in bottom waters. Sensitive laminated sites may play the important role of a `canary in the coal mine' where monitoring the character and geographical extent of laminations/varves serves as a diagnostic tool to judge environmental trends. Analyses of modern varve records will gain importance for simultaneously providing high-resolution and longer-term perspectives. Especially in regions with limited resources or at remote sites, the comparatively low cost of high-resolution sediment analyses for environmental monitoring is an essential advantage over continuous monitoring of oceanographic conditions in the water column.

A major change in North Atlantic deep water circulation during the Early Pleistocene transition 1.6 million years ago

NASA Astrophysics Data System (ADS)

Khélifi, N.; Frank, M.

2013-12-01

The global ocean-climate system has been highly sensitive to the formation and advection of deep water in the North Atlantic but its evolution over the Pliocene-Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters are not well constrained. Here we present new records of the bottom-water radiogenic neodymium isotope (ϵNd) variability obtained from three DSDP/ODP sites at water depths between 2100 and 5000 m in the Northeast Atlantic to reconstruct changes in deep water circulation over the past 4 million years. Prior to 1.6 million years ago (Ma), we find ϵNd values primarily oscillating between -9 and -11 at all sites, consistent with enhanced vertical mixing of water masses. At 1.6 Ma, the ϵNd signatures synchronously shifted to less radiogenic values around -12 at different water depths and water mass signatures gradually became more distinct. Since then values and amplitudes of "glacial/interglacial" ϵNd oscillations have been similar to the Late Quaternary at each site. This change 1.6 Ma reflects a major reorganization of deep water circulation in the Northeast Atlantic towards a more stratified water column with distinct water masses accompanying the enhanced response of climate to the Earth's obliquity forcing during the Early Pleistocene transition.

Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

NASA Technical Reports Server (NTRS)

Drinkwater, Mark R.

1999-01-01

Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of enhanced poleward wind stress reduce ice growth by compacting the ice along the coastline and closing open water in leads and polynyas. Model simulations confirm that years of low ice production, such as 1991, coincide with years of lower than normal bottom water outflow. Future plans include the assimilation of satellite ice concentrations and ice drift dynamics to more accurately constrain boundary conditions in the model.

Dense Winter Water Mass Formation In The Northwestern Pacific Marginal Seas:

NASA Astrophysics Data System (ADS)

Talley, L.; Lobanov, V.; Tishchenko, P.; Shcherbina, A.; Rudnick, D.; Salyuk, A.; Sagalaev, S.; Ponomarev, V.; Zhabin, I.

Two separate winter water mass formation experiments were carried out in the north- western Pacific. The Japan/East Sea (JES) is well-ventilated to the bottom (3500 m depth), and is much better ventilated than the adjacent North Pacific at the same depth and density. Winter data from 1999 and 2000 show that the JES is one of the few sites in the world with deep winter convection, and that convection in the JES has many similarities to convection in the Mediterranean. It was shown previously that deep oxygen in the JES has been declining over many decades, suggesting that ventilation was more vigorous early in the 20th century than in recent decades. Nevertheless, the presence of significant oxygen and chlorofluorocarbons to the JES bottom suggests ongoing ventilation. In winter, 1999, a first late-winter survey of the northern JES included one hydrographic station with evidence of open-ocean convection to about 1100 meters in the cold air outbreak region south of Vladivostok, and weak evidence of brine rejection under ice formation in Peter the Great Bay (shelf near Vladivos- tok). Topography and the presence of a semi-permanent anticyclonic eddy and the subpolar front delineate the convection region, which is in the path of strong northerly winter winds. Persistently colder conditions in winter 2000, including Vladivostok air temperatures colder than any other year since 1976 and SST -2C below normal in the northern Japan Sea, showed widespread convection. Significant bottom water was created through brine rejection in Peter the Great Bay and was found the base of the continental slope south of Vladivostok. Ventilation of North Pacific Intermediate Water occurs in the Okhotsk Sea, through brine rejection during sea ice formation, in polynyas on the northwest shelf. Moored observations on the shelf during winter 1999-2000 showed the creation of dense shelf water at 26.95 sigma_theta and clear evidence of brine rejection through the winter. The 1999 deployment hydrographic survey shows cold, dense water from the shelf at 26.95 sigma_theta. The lower density shelf water in June 2000 compared with Septem- ber 1999 is consistent with the reduced severity of winter 2000. Outflow of the densest cold water of shelf origin in both the 1999 and 2000 CTD surveys was located slightly inshore of the axis of the deepest channel between Sakhalin and Kashevarov Bank.

Trace-element deposition in the Cariaco Basin, Venezuela Shelf, under sulfate-reducing conditions: a history of the local hydrography and global climate, 20 ka to the present

USGS Publications Warehouse

Piper, David Z.; Dean, Walter E.

2002-01-01

A sediment core from the Cariaco Basin on the Venezuelan continental shelf, which recovered sediment that has been dated back to 20 ka (thousand years ago), was examined for its major-element-oxide and trace-element composition. Cadmium (Cd), chromium (Cr), copper (Cu), molybdenum (Mo), nickel (Ni), vanadium (V), and zinc (Zn) can be partitioned between a siliciclastic, terrigenous-derived fraction and two seawater-derived fractions. The two marine fractions are (1) a biogenic fraction represented by nutrient trace elements taken up mostly in the photic zone by phytoplankton, and (2) a hydrogenous fraction that has been derived from bottom water via adsorption and precipitation reactions. This suite of trace elements contrasts with a second suite of trace elements—barium (Ba), cobalt (Co), gallium (Ga), lithium (Li), the rare-earth elements, thorium (Th), yttrium (Y), and several of the major-element oxides—that has had solely a terrigenous source. The partitioning scheme, coupled with bulk sediment accumulation rates measured by others, allows us to determine the accumulation rate of trace elements in each of the three sediment fractions and of the fractions themselves. The current export of organic matter from the photic zone, redox conditions and advection of bottom water, and flux of terrigenous debris into the basin can be used to calculate independently trace-element depositional rates. The calculated rates show excellent agreement with the measured rates of the surface sediment. This agreement supports a model of trace-element accumulation rates in the subsurface sediment that gives a 20-kyr history of upwelling into the photic zone (that is, primary productivity), bottom-water advection and redox, and provenance. Correspondence of extrema in the geochemical signals with global changes in sea level and climate demonstrates the high degree to which the basin hydrography and provenance have responded to the paleoceanographic and paleoclimatic regimes of the last 20 kyr. The accumulation rate of the marine fraction of Mo increased abruptly at about 14.8 ka (calendar years), from less than 0.5 µg cm-2 yr-1 to greater than 4 µg cm-2 yr-1. Its accumulation rate remained high but variable until 8.6 ka, when it decreased sharply to 1 µg cm-2 yr-1. It continued to decrease to 4.0 ka, to its lowest value for the past 15 kyr, before gradually increasing to the present. Between 14.8 ka and 8.6 ka, its accumulation rate exhibited strong maxima at 14.4, 13.0, and 9.9 ka. The oldest maximum corresponds to melt-water pulse IA into the Gulf of Mexico. A relative minimum, centered at about 11.1 ka, corresponds to melt-water pulse IB; a strong maximum occurs in the immediately overlying sediment. The maximum at 13.0 ka corresponds to onset of the Younger Dryas cold event. This pattern to the accumulation rate of Mo (and V) can be interpreted in terms of its deposition from bottom water of the basin, the hydrogenous fraction, under SO42- -reducing conditions, during times of intense bottom-water advection 14.8 ka to 11.1 ka and significantly less intense bottom-water advection 11 ka to the present. The accumulation rate of Cd shows a pattern that is only slightly different from that of Mo, although its deposition was determined largely by the rain rate of organic matter into the bottom water, a biogenic fraction whose deposition was driven by upwelling of nutrient-enriched water into the photic zone. Its accumulation exhibits only moderately high rates, on average, during both melt-water pulses. Its highest rate, and that of upwelling, occurred during the Younger Dryas, and again following melt-water pulse IB. The marine fractions of Cu, Ni, and Zn also have a strong biogenic signal. The siliciclastic terrigenous debris, however, represents the dominant source, and host, of Cu, Ni, and Zn. All four trace elements have a consid-erably weaker hydrogenous signal than biogenic signal. Accumulation rates of the terrigenous fraction, as reflected by accumulation rates of Th and Ga, show strong maxima at 16.2 and 12.7 ka and minima at 14.1 and 11.1 ka. Co, Li, REE, and Y have a similar distribution. The minima occurred during melt-water pulses IA and IB, the maxima during the Younger Dryas and the rise in sea level following the last glacial maximum.

High resolution mapping of hydrothermal plumes in the Mariana back-arc relate seafloor sources to above-bottom plumes

NASA Astrophysics Data System (ADS)

Walker, S. L.; Baker, E. T.; Resing, J. A.; Chadwick, W. W., Jr.; Merle, S. G.; Kaiser, C. L.

2016-12-01

The Mariana backarc spreading center between 12.9°-18°N was systematically explored for hydrothermal activity in Nov-Dec 2015 (R/V Falkor cruise FK151121) by conducting long distance along-axis CTD tows (vertical range was 20-600 meters above bottom (mab)) followed by higher resolution, horizontal grid AUV Sentry surveys at 70 mab in some of the areas where plumes were found. In those areas, the combination of along-axis CTD tows and near-bottom AUV surveys provides a nearly 3-dimensional view of the above-bottom plume relative to the seafloor morphology and potential sources. In addition, photo surveys were run at 5 mab at two of the sites. At 15.4°N, strong ORP anomalies (ΔE=-39 mv) with weak to absent optical signals were aligned with a new (<3yr) lava flow, suggesting widespread diffuse venting was associated with still-cooling lava to create a broad, optically weak plume that extended to 500 mab. About 10 km north of the new lava flow (15.5°N) there were fewer, but more distinct instances where temperature, particle, and OPR anomalies were co-located at 70 mab, providing information for the likely locations where more focused, higher temperature venting generated an optically intense (dNTU=0.032) above-bottom plume (to 500 mab over the axial high). The plume over the backarc segment high at 17.0°N exhibited a significant optical anomaly (dNTU=0.023) with a very strong ORP anomaly (ΔE=-88 mv) that extended only 1.5 km along-axis. The near-bottom survey showed a broad area ( 3km2) with robust temperature, particle, and ORP signals. Directed by this information, and the high resolution bathymetry acquired from the AUV survey, several active chimneys (one being 30 m tall with temperatures up to 340°C) were found during NOAA Okeanos Explorer ROV dives in May 2016. At 18°N, anomalies seen in the 11 km2 AUV survey were generally located along the axis of the spreading center and, with one exception, were limited to areas of previously-known (1987) venting. The plume in the water column over the Burke vent site was defined by both particle (dNTU=0.010) and ORP (ΔE=-11 mv) anomalies from 400-800 mab, but only ORP signals 120-400 mab. ORP signals were seen over the other sites without any optical anomalies; the much lower rise heights (200-400 mab) suggest only lower temperature, diffuse venting persists at these sites.

Properties of perpendicular-anisotropy magnetic tunnel junctions fabricated over the bottom electrode contact

NASA Astrophysics Data System (ADS)

Miura, Sadahiko; Honjo, Hiroaki; Kinoshita, Keizo; Tokutome, Keiichi; Koike, Hiroaki; Ikeda, Shoji; Endoh, Tetsuo; Ohno, Hideo

2015-04-01

Perpendicular-anisotropy magnetic tunnel junctions (MTJs) were prepared on four substrate geometries, i.e., directly on the axis of the bottom electrode contact, directly off the axis of the bottom electrode contact, on the axis of the bottom electrode contact with a polished bottom electrode, and off the axis of the bottom electrode contact with a polished bottom electrode. Electrical shorts were observed for direct on-axis geometry at a certain extent, whereas there were no electrical shorts for the other three geometries. The MR ratio/σR, JC0, and thermal stability factor of the devices for polish on-axis geometry were almost the same as those for polish off-axis geometry. From TEM observations of the polish on-axis device, the interface between the bottom contact and the base electrode was determined to be rough, whereas the MgO barrier layer was determined to be smooth, indicating that the polish process was effective for smooth magnetic tunnel junction fabrication over the bottom contact. MTJs for polish on-axis geometry eliminated the base electrode resistance and increased the magnetoresistance ratio. This technology contributes to the higher density of spin transfer torque magnetic random access memory.

Field screening of water quality, bottom sediment, and biota associated with irrigation drainage in and near Walker River Indian Reservation, Nevada 1994-95

USGS Publications Warehouse

Thodal, Carl E.; Tuttle, Peter L.

1996-01-01

A study was begun in 1994 to determine whether the quality of irrigation drainage from the Walker River Indian Reservation, Nevada, has caused or has potential to cause harmful effects on human health or on fish and wildlife, or may adversely affect the suitability of the Walker River for other beneficial uses. Samples of water, bottom sediment, and biota were collected during June-August 1994 (during a drought year) from sites upstream from and on the Walker River Indian Reservation for analyses of trace elements. Other analyses included physical characteristics, major dissolved constituents, selected species of water-soluble nitrogen and phosphorus, and selected pesticides in bottom sediment. Water samples were collected again from four sites on the Reservation in August 1995 (during a wetterthan- average year) to provide data for comparing extreme climatic conditions. Water samples collected from the Walker River Indian Reservation in 1994 equaled or exceeded the Nevada water-quality standard or level of concern for at least one of the following: water temperature, pH, dissolved solids, unionized ammonia, phosphate, arsenic, boron, chromium, lead, and molybdenum; in 1995, only a single sample from one site exceeded a Nevada water-quality standard for molybdenum. Levels of concern for trace elements in bottom sediment collected in 1994 were equaled or exceeded for arsenic, iron, manganese, and zinc. Concentrations of organochiorine pesticide residues in bottom sediment were below analytical reporting limits. Levels of concern for trace-elements in samples of biota were equaled or exceeded for arsenic, boron, copper, and mercury. Results of toxicity testing indicate that only water samples from Walker Lake caused a toxic response in test bacteria. Arsenic and boron concentrations in water, bottom sediment, and biological tissue exceeded levels of concern throughout the Walker River Basin, but most commonly in the lower Walker River Basin. Mercury also was elevated in several biological samples collected throughout the Basin, although concentrations in water and bottom sediment were below analytical reporting limits. Sources of arsenic, boron, and mercury in the Basin are uncertain, but ambient levels reported for a variety of sample matrices collected from western Nevada generally exceed ranges cited as natural background levels. Because these potentially toxic constituents exceeded concern levels in areas that do not directly receive irrigation drainage, concentrations measured in samples collected for this study may not necessarily be attributable to agricultural activities. Diversion of river water for irrigation may have greater effects on beneficial uses of water and on fish and wildlife than does drainage from agricultural areas on the Reservation. In 1994, agricultural water consumption precluded dilution of ground-water seepage to the river channel. This resulted in concentrations of potentially toxic solutes that exceeded levels of concern. Diversion of irrigation water also may have facilitated leaching of potentially toxic solutes from irrigated soil on the Reservation, but during this study all water applied for irrigation on the Reservation was either consumed by evapotranspiration or infiltrated to recharge shallow ground water. No irrigation drainage was found on the Reservation during this study. However, because 1994 samples of ground-water seepage to the Walker River channel exceeded at least six Nevada waterquality standards, water-quality problems may result should ground-water levels rise enough to cause ground-water discharge to the agricultural drain on the Reservation. Nevertheless, the potential for adverse effects from irrigation drainage on the Reservation is believed to be small because surface-water rights for the Walker River Indian Reservation amount to only 2 percent of total surface- water rights in the entire Walker River Basin.

Sediment deposition and selected water-quality characteristics in Cedar Lake and Lake Olathe, Northeast Kansas, 2000

USGS Publications Warehouse

Mau, D.P.

2002-01-01

The Lake Olathe watershed, located in northeast Kansas, was investigated using bathymetric survey data and reservoir bottom-sediment cores to determine sediment deposition, water-quality trends, and transport of nutrients (phosphorus and nitrogen species), selected trace elements, selected pesticides, and diatoms as indicators of eutrophic (organic-enriched and depleted oxygen supply) conditions. To determine sediment deposition and loads, bathymetric data from Cedar Lake and Lake Olathe, both located in the Lake Olathe watershed, were collected in 2000 and compared to historical topographic data collected when the lakes were built. Approximately 338 acre-feet of sediment deposition has occurred in Cedar Lake since dam closure in 1938, and 317 acre-feet has occurred at Lake Olathe since 1956. Mean annual sediment deposition was 5.45 acre-feet per year (0.89 acre-feet per year per square mile) for Cedar Lake and 7.0 acre-feet per year (0.42 acre-feet per year per square mile) for Lake Olathe. Mean annual sediment loads for the two reservoirs were 9.6 million pounds per year for Cedar Lake and 12.6 million pounds per year for Lake Olathe. Mean concentrations of total phosphorus in bottom-sediment samples from Cedar Lake ranged from 1,370 to 1,810 milligrams per kilogram, and concentrations in bottom-sediment samples from Lake Olathe ranged from 588 to 1,030 milligrams per kilogram. The implication of large total phosphorus concentrations in the bottom sediment of Cedar Lake is that inflow into Cedar Lake is rich in phosphorus and that adverse water-quality conditions could affect water quality in downstream Lake Olathe through discharge of water from Cedar Lake to Lake Olathe via Cedar Creek. Mean annual phosphorus loads transported from the Lake Olathe watershed were estimated to be 14,700 pounds per year for Cedar Lake and 9,720 pounds per year for Lake Olathe. The mean annual phosphorus yields were estimated to be 3.74 pounds per acre per year for Cedar Lake and 0.91 pound per acre per year for Lake Olathe. Phosphorus yields in the Cedar Lake watershed were largest of the six Kansas impoundment watersheds recently studied. Concentrations of total ammonia plus organic nitrogen as nitrogen in bottom sediment increased from upstream to downstream in both Cedar Lake and Lake Olathe. Mean concentrations of total ammonia plus organic nitrogen as nitrogen (N) ranged from 2,000 to 2,700 milligrams per kilogram in bottom-sediment samples from Cedar Lake and from 1,300 to 2,700 milligrams per kilogram in samples from Lake Olathe. There was no statistical significance between total ammonia plus organic nitrogen as nitrogen and depth of bottom sediment. Concentrations of six trace elements in bottom sediment from Cedar Lake and Lake Olathe (arsenic, chromium, copper, lead, nickel, and zinc) exceeded the U.S. Environmental Protection Agency Threshold Effects Levels (TELs) sediment-quality guidelines for aquatic organisms in sediment except for one lead concentration. Probable Effects Levels (PELs) for trace elements, however, were not exceeded at either lake. Organochlorine and organophosphate insecticides were not detected in bottom-sediment samples from either Cedar Lake or Lake Olathe, but the acetanilide herbicides alachlor and metolachlor were detected in sediment from both lakes. The U.S. Environmental Protection Agency has not proposed TEL or PEL guideline concentrations for bottom sediment for any of the organophosphate, acetanilide, or triazine pesticides. The diatoms (microscopic, single-celled organisms) Cyclotella bodanica, an indicator of low organic-enriched water, and Cyclotella meneghiniana, an indicator of organic-enriched water, were both present in bottom sediment from Lake Olathe. The presence of both of these diatoms suggests varying periods of low and high eutrophication in Lake Olathe from 1956 to 2000. The concentrations of two species in bottom sediment from Cedar Lake, Aulacoseira cf alpigena and Cyclotella meneg

The bubble method of water purification

NASA Astrophysics Data System (ADS)

Smirnov, B. M.; Babaeva, N. Yu.; Naidis, G. V.; Panov, V. A.; Saveliev, A. S.; Son, E. E.; Tereshonok, D. V.

2018-02-01

The processes of water purification from admixture molecules are analyzed. The purification rate is limited due to a low diffusion coefficient of the admixture molecules in water. At non-small concentrations of the admixture molecules, the water purication can proceed through association of molecules in condensed nanoparticles which fall on the bottom of the water volume. The rate of association may be increased in an external electric field, but in reality this cannot change significantly the rate of the purification process. The bubble method of water purification is considered, where air bubbles formed at the bottom of the water volume, transfer admixture molecules to the interface. This method allows one to clean small water volumes fast. This mechanism of water purification is realized experimentally and exhibits the promises of the bubble purification method.