Field assessment of sediment traps

Sediment traps whose particle collection abilities had been calibrated in a laboratory flume at velocities of 0, 4, and 9 cm/sec were deployed in natural bodies of water to intercalibrate larger traps under current conditions ranging from tranquil to over 20 cm/sec. For cylinders, the height to width ratio is the controlling factor of the mass of sediment collected. Traps can be scaled up in size and maintain a similar (though not necessarily correct) collection rate...

Electrical resistivity and Hall effect in sodium tungsten bronze

The electrical resistivity and Hall coefficient of sodium tungsten bronze have been measured as a function of sodium concentration and temperature. Measurements were on single crystals with values of x between 0.58 and 0.90, where x is the x in NaxWO3;The room temperature resistivity possessed a minimum value of (3.20 +/- 0.14) x 10-5 ohm-cm. at x = 0.75 in agreement with previously reported results. The resistivity was (12.5 +/- 0.23) x 10-5 ohm-cm. at x = 0.584 and (5.89 +/- 0.20) x 10-5 ohm-cm. at x = 0.863;The resistivity was linear with temperature in the range 125°K. to 300°K. The temperature coefficient of resistivity was also a minimum at x = 0.75. The value of the temperature coefficient of resistivity at that concentration was (9.45 +/- 0.60) x 10-8 ohm-cm./°C. The residual resistivity was obtained by extrapolation of the resistivity to absolute zero. The residual resistivity was a minimum at x = 0.75 with a value of (1.25 +/- 0.10) x 10-5 ohm-cm;The Hall coefficient varied less than 2 percent with temperature in the range 78°K. to 370°K. The Hall coefficient was inversely proportional to the sodium concentration, varying from -(6.10 +/- 0.15) x 10-4 cm.3/coulomb at x = 0.584 to -(4.07 +/- 0.03) x 10-4 cm.3/coulomb at x = 0.897. The values for the Hall coefficient corresponded very nearly to one free electron for each sodium atom;The minimum in the curve of resistivity as a function of sodium concentration is due to an anomalous maximum in the electron mobility at x = 0.75. The reasons for this anomaly are not clearly understood

Fluxes, dynamics and chemistry of particulates in the ocean

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October, 1977.Sediment traps designed to yield quantitative data of particulate fluxes have been deployed and successfully recovered on four moorings in the deep sea. The traps were designed after extensive calibration of different shapes of containers. Further intercalibration of trap design was made in field experiments over a range of current velocities. Experiments with Niskin bottles showed that concentrations of suspended particulate matter obtained with standard filtration methods were low and had to be increased by an average factor of 1.5 to correct for particles settling below the sampling spigot. The trap arrays were designed to sample the particulate fluxes both immediately above and within the nepheloid layer. The data derived from the traps have been used to estimate vertical fluxes of particles including, for the first time, an attempt to distinguish between the flux of material settling from the upper water column (the "primary flux") and material which has been resuspended from some region of the sea floor (resuspension flux). From these data and measurements of the net nepheloid standing crop of particles one can also estimate a residence time for particles resuspended in the nepheloid layer. This residence time appears to be on the order of days to weeks in the bottom 15 m of the water column and weeks to months in the bottom 100 m. Between 80% and 90% of the particles collected in the six traps where particle size was measured were less than 63 μm. The mean size of particles collected in the nepheloid layer was about 20 μm, and above the nepheloid layer the mean was 11 μm. Less than 3% of the organic carbon produced in the photic zone at the trap sites was collected as primary flux 500 m above the sea floor. The primary flux measured at two sites was enough to supply 75% on the upper Rise and 160% on the mid Rise of the organic carbon needed for respiration and for burial in the accumulating sediments. From an intercomparison of the composition of particles falling rapidly (collected in traps), falling slowly or not at all (collected in water bottles), and resting on the sea floor (from a core top), it was determined that elements associated with biogenic matter, such as Ca, Sr, Cu, and I, were carried preferentially by the particles falling rapidly. Once the particles reached the bottom, the concentration of those elements was decreased through decomposition, respiration, or dissolution. Dissolution appears rapid in the vicinity of the sea floor, because despite an abundance of radiolarians, diatoms, and juvenile foraminifera collected in all traps, these forms were rare in core samples. The dynamic nature of thenepheloid layer makes it possible for particles to be resuspended many times before they are finally buried. This enables sediment to be carried long distances from its origin. The recycling of particles near the sea floor may increase dissolution of silicious and carbonate matter.Financial aid was provided in the form of a research assistantship from the Office of Naval Research through MIT and WHOI

Sediment trap dynamics and calibration: A laboratory evaluation

The flow dynamics and particle trapping characteristics of several designs of sediment traps were investigated using dye, sea-water, and deep-sea !utite in a recirculating flume and fish tank at velocities of 0, 4, and 9 cm/sec. Particles are collected through a process of fluid exchange rather than falling freely into a trap. The efficiency of a trap is therefore a function of the residence time and circulation pattern of fluid within the trap, processes which are controlled primarily by trap geometry and secondarily by current velocity...

The effect of brine on the collection efficiency of cylindrical sediment traps

Cylindrical sediment traps are frequently used to measure the downward flux of particles in the upper ocean. Some protocols recommend filling these traps with brine (50 psu in excess of ambient) before deployment to better retain the collected sample. However, this also changes the aspect ratio of the traps—a critical parameter affecting the trapping efficiency. We conducted controlled experiments in a flume that demonstrate filling traps with a 5 psu brine decreases their trapping efficiency to 54% at a velocity of 5 cm sec−1, and to 75% at 15 cm sec−1 relative to the same trap with no brine. This suggests that a revision of the protocols and further experiments are needed

Sedimentation rates in the slope water of the northwest Atlantic Ocean measured directly with sediment traps

Four sedi ment trap arrays we re deployed in the Slope Water off the northeast United States for periods of 5.8 to 15.8 days from May to August 1976. Three traps, each a PVC cylinder 25 cm in diameter and 76 cm tall, were attached a t va rious distances above the bottom along bottom-anchored moorings. Closure of the individu al traps and release of each array from its expend able anchor was co ntrolled by a Williams Timed Release or an AMF acoustic release. DSRV ALVIN, making observations of one array, closed those traps and released that array from the bottom...

Observations on the degradation of biogenic material in the deep ocean with implications on accuracy of sediment trap fluxes

The results of several observations and experiments indicate that the decay of organic material inside and outside of sediment traps in the deep ocean is on the order of 0.1-1.0% day−. These results must be considered when using sediment traps to determine the flux of organic material through the water column. The effectiveness of poisons in traps has not been adequately determined since the concentration of poisons in traps has not been monitored. Even traps containing poison may lose organic matter through leaching or from rapid grazing. A model is presented to quantify the loss of organic carbon at different decay rates and to determine optimum length of trap deployments

Plans and Specifications for a Sewerage System for all of Corvallis Lying West of Ninth Street

At the present time only a portion of Corvallis is sewered and a portion of the city still employs the most crude and unhealthful methods of disposal. The district east of Ninth Street, as shown on the map, has an effective system of well constructed sewers, of the combined storm-water and domestic sewage type. Upon investigation, however, it was found that this system is already connected up with more territory than it was originally designed to drain, and that a further extension of them would be impractical. With the added territory which has been connected with these mains, they are now taxed almost to their limit, and further extension might produce serious results. The problem, then, for consideration was to design a system or systems which will drain the city districts west of Ninth Street and provide for the needs in the future

A sediment trap experiment in the Vema Channel to evaluate the effect of horizontal particle fluxes on measured vertical fluxes

Sediment traps are used to measure fluxes and collect samples for studies in biology, chemistry and geology, yet we have much to learn about factors that influence particle collection rates. Toward this end, we deployed cylindrical sediment traps on five current meter moorings across the Vema Channel to field-test the effect of different horizontal particle fluxes on the collection rate of the traps— instruments intended for the collection of vertically settling particles. The asymmetric flow of Antarctic Bottom Water through the Vema Channel created an excellent natural flume environment in which there were vertical and lateral gradients in the distribution of both horizontal velocity and particle concentration and, therefore, the resulting horizontal flux. Horizontal effects were examined by comparing quantities of collected material (apparent vertical fluxes) with the horizontal fluxes of particles past each trap. We also looked for evidence of hydrodynamic biases by comparing and contrasting the composition of trap material based on particle size and the concentration of Al, Si, Ca, Mg, Mn, Corg and CaCO3. Experimental inverted traps and traps with only side openings were deployed to test a hypothesis of how particles are collected in traps. The vertical flux of surface-water particles should have been relatively uniform over the 45 km region of the mooring locations, so if horizontal transport contributed significantly to collection rates in traps, the calculated trap fluxes should be correlated positively with the horizontal flux. If the horizontal flow caused undertrapping, there should be a negative correlation with velocity or Reynolds number. The gross horizontal flux past different traps varied by a factor of 37, yet the quantity collected by the traps differed by only a factor of 1.4. The calculated horizontal fluxes were 2–4 orders of magnitude larger than the measured apparent vertical fluxes. Mean velocities past the traps ranged from 1–22 cm s−1 (Reynolds numbers of 3,500–43,000 for these traps with a diameter of 30.5 cm and an aspect ratio of ≈3) and showed no statistically significant relationship to the apparent vertical flux. We conclude that at current speeds measured in a very large portion of the world\u27s oceans, vertical fluxes measured with moored, cylindrical traps should exhibit little effect from horizontal currents

On the transport and modification of Antarctic Bottom Water in the Vema Channel

The Verna Channel is a deep passage across the Rio Grande Rise in the South Atlantic through which Antarctic Bottom Water (AABW) must flow on its way northward from the Argentine Basin to the Brazil Basin and eventuafly into the North Atlantic…