Seafloor sediments

Barite and sphalerite tend to precipitate at lower temperature from the hydrothermal solution mixed with a large amount of cold seawater (but mixing ratio (seawater/hydrothermal solution) may be less than 0.2). These minerals precipitate on the seafloor and/or at very shallow subsurface environment. However, chalcopyrite tends to precipitate from high temperature solutions in ore bodies and/or at the sub-seafloor sediments. Usually shale which is relatively impermeable overlies the Besshi-type ore bodies. This suggests that hydrothermal solution could not issue from the seafloor and... 

Arsenic removal from seawater to sediments is mainly governed by pyrite formation in the seafloor sediments. Production rate of sedimentary pyrite is 2.5 x 10 g S/year (Holland, 1978). Therefore, As removal by pyrite from seawater is (1.3-2.9) x lO g/year. This is the same order of magnitude as As input to ocean by river which is equal to 0.7 x 10 g/year. 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

Fig. 9.6 Climate records from the Vostok Antarctic ice core and the tropical carbonate seafloor sediment core V19-30 (Shakleton, N. J. and Pisais, N. Am. Geophys. Union, Geophys. Mon. 3, 303 (1985))...

The same phenomenology must be important locally on Earth, too, where thick evaporite deposits of hydrated salts and local thick beds of methane clathrate in permafrost or seafloor sediments should influence the thermal environment of the crust. The predicted control on the crust s thermal state by hydrate deposits should have consequences for the localization of hydrothermal springs around and within evaporite basins, hydrothermal metamorphism... 

Patterson, D. B., Farley, K. A. (1998) Extraterrestrial 3He in seafloor sediments Evidence for correlated lOOkyr periodicity in the accretion rate of interplanetary dusts, orbital parameters, and Quaternary climate. Geochim. Cosmochim. Acta, 62, 3669-82. 

Sinking rates of marine snow, however, are greater than 100 md (Shanks and Trent, 1980 Alldredge and Gotschalk, 1989). Transit time to the deep in this case is days to weeks, which agrees with observations of a close temporal coupling between surface production and seafloor sedimentation (e.g., Billett et al, 1983 Asper et al, 1992). 

Hales B., Burgess L., and Emerson S. (1997) An absorbance-based fiber-optic sensor for C02(aq) measurements in pore waters of seafloor sediments. Mar. Chem. 59, 51-62. 

Farley K. A. (2001) Extraterrestrial helium in seafloor sediments identification, characteristics and accretion rates over geologic time. In Accretion of Extraterrestrial Matter throughout Earth s History (eds. B. Peucker-Ehrenbrinck and B. Schmitz). Kluwer, New York, pp. 179-204. 

X HE LEVELS OF INDUSTRIAL CHEMICAL WASTES BEING DUMPED into our nation s coastal waters are constantly being monitored by the National Oceanic and Atmospheric Administration (NO A A). To carry out the frequent marine monitoring programs necessary to stay abreast of this problem, it was determined in 1977 that more expedient shipboard sampling and analyses systems would have to be developed. One area of prime interest for sampling and scrutiny was the surficial seafloor sediments. To enhance rapid data collection, the ability to analytically measure samples while at sea was essential. This capability would allow areas of interest to be delineated and studied in detail before the survey vessel returned to port. 

To obtain as much data as possible, the system needed a continuous sampling capability. Also, to fulfill the requirement of rapid data analyses while at sea, nondestructive elemental analysis was selected for the method of shipboard analysis. A sampling and analysis system called the continuous seafloor sediment sampler (CS ) was developed from this work. 

The CS system is made up of three major components a seafloor sediment sampler, shipboard sample processor, and nondestructive elemental analysis instrumentation. It was described in detail previously (8). Design requirements for the seafloor sediment sampler are that it be in constant contact with the seafloor while being towed at speeds up to 6 knots, agitate only the upper surficial seafloor sediment and create a plume, contain a pumping means to sample the sediment slurry plume, and be capable of transporting the sediment slurry to a surface ship. These conditions were achieved by designing a towable sled that contained, within its structure, a submersible pump that was hose-connected to the surface ship. 

After the testing and evaluation of the operational parameters of the sediment retrieval system, the ground-truth study of the CS system was initiated to determine whether the CS samples reflected the true sediment composition and, therefore, its ability to correctly and rapidly survey the seafloor sediment. 

The final phase in the development of the CS system was to test and evaluate the capability of the CS system to analytically portray the true elemental content of the seafloor sediments. To carry out this task, a joint Center for Applied Isotope Studies (CAIS)-NOAA ground-truth study was initiated. A site for the study was selected in the Baltimore Harbor (Maryland) along the Patapsco River, south of North Point and adjacent to the Brewer-ton Channel see Figure 7 ). This site is a discontinued spoil area with documented high levels of heavy metals in the sediments. Water depths of this site are 15-25 m, well within the operational range of the CS system, and it is located close to available NO A A facilities. 

Sediment sampling of the seven stations using the CS equipment was carried out by running transects with the survey vessel parallel to, and as close as possible to, the marker buoys. The CS underwater seafloor sediment sampler was pulled at a speed of three knots and, when abreast of each buoy, the sediment collected was recorded as being from that station. The sediment wafers prepared aboard ship from the collected slurries were immediately analyzed by XRF for three elements (Mn, Fe, and Ti) and were stored for further land-based analyses of other elements. A comparison of the elemental content of the sediments collected from the seven stations by box coring and with the use of the CS equipment constituted the basis for ground-truth evaluation of the CS system. 

Hydrocarbons in Seafloor Sediments Correlations between Geochemistry, Seismic Structure, and Possible Reservoired Oil and Gas, in Proceedings 1975 Offshore Technology Conference, Volume III, 65-70. 

Methane is produced from acetate at extremely low rates in deep sub-seafloor sediments. The process can be measured experimentally using a radioactive isotope, C-acetate. How can the experiment be designed to obtain the highest sensitivity and detect the low rate ... 

Piper, D.Z., Swint, T.R., Sullivan, L.G and McCoy, F.W., 1985. Manganese nodules, seafloor sediment, and sedimentation rates in the Circum-Pacific region. Circum-Pacific Council for Energy and Mineral Resources Circum-Pacific Map Project. American Association of Petroleum Geologists, Tulsa, Oklahoma. 

Farley KA (2001) Extraterrestrial helium in seafloor sediments Identification, characteristics, and accretion rate over geological time. In Accretion of extraterrestrial matter throughout Earth s history. B Peucker-Ehrenbrink, B Schmitz (eds) Kluwer Academic/Plenum Pubhsheis, p 179-204 Farley KA, Patterson DB (1995) A 100-kyr periodicity in the flux of extraterrestrial e to the sea floor. Nature 378 600-603... 

Farley KA, Mirkhopadhyay S, Eltgroth S (2001) Assessment of the distribution of time in seafloor sediments using extraterrestrial He. EOS Trans Am Geophys Urrion Fall Mtg Suppl 82 F1140... 

Microscopic examination of seafloor sediments (if shallow enough that the CaCOs does not dissolve) and of material caught in sediment traps has revealed that much of the calcium carbonate in the samples consists of coccoliths. The flux of coccoliths probably accounts for c. 50% of the total vertical CaCOs flux in open ocean waters (in other words, about 50% of the inorganic carbon pump), with foraminifera shells responsible for most of the rest. It is usually not the most numerous species (E. huxleyi) but rather larger species (e.g., Calci-discus quadriperforatus and Coccolithus pelagicus) that make the greatest contributions to the total coccolith flux. 

Scatter in the data shown in Fig. 1 could be due to several factors, such as variable diffusion coefficients, sample intervals too widely spaced to accurately indicate gradients, poorly constrained sedimentation rates, failure to recover seafloor sediments in cores and consequent depth inaccuracies, an oxidizing (bioturbated) zone near the seafloor, advective supply of sulfate at depth and intense anaerobic methane oxidation. 

---