Deep-sea Surface Sediments Research Articles

The distribution of 230Th and 231Pa in the deep-sea surface sediments of the Pacific Ocean

In order to determine the areal extent and distribution of 231Pa sinks in the Pacific Ocean, we have analyzed 34 deep-sea surface sediment samples from widely distributed locations for their Pa, Th and U isotopes. While the 230Th xs content varies by more than a factor often, the 231Pa xs content is confined in a relatively narrow range with a mean value of 2.8 ± 1.4 dpm/g. There is a positive correlation between 230Th xs and 231Pa xs and, using the regression line it is possible to calculate the ( 230Th xs 231Pa xs ) activity ratios in samples for which only 230Th data are available. We then constructed a map of ( 230Th xs 231Pa xs ) distribution. Using ( 230Pa xs 231Pa xs ) < 11 (the production ratio in the water column) as a criterion for identifying preferential 231Pa sinks, we have identified an area covering 30–40% of the Pacific Ocean. This area includes most of the Pacific margins, the northwest Pacific, the Antarctic Ocean and perhaps the mid-ocean ridge regions, and is nearly coincident with that of high sediment accumulation rates: this suggests that the paniculate flux is important for the removal of 231Pa from the ocean. Two models for the removal of 231Pa produced in the open ocean are: 1. (1) lateral transport into the vertical flux in regions of high particulate flux ( Damaster, 1979; Anderson et al, 1983a,b) or 2. (2) uptake at the sediment-water boundary: the second model is more likely to be correct. To distinguish unequivocally between the two proposed models, we would need sediment trap data for the western North Pacific.

Distribution of biogenic silica and quartz in recent deep-sea sediments

Research Article| March 01, 1986 Distribution of biogenic silica and quartz in recent deep-sea sediments Margaret Leinen; Margaret Leinen 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197 Search for other works by this author on: GSW Google Scholar Douglas Cwienk; Douglas Cwienk 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197 Search for other works by this author on: GSW Google Scholar G. Ross Heath; G. Ross Heath 2College of Ocean and Fishery Sciences, University of Washington HA-40, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Pierre E. Biscaye; Pierre E. Biscaye 3Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar V. Kolla; V. Kolla 4Elf Aquitaine Petroleum, Allied Bank Plaza, 1000 Louisiana Avenue, Suite 3800, Houston, Texas 77002 Search for other works by this author on: GSW Google Scholar Jørn Thiede; Jørn Thiede 5Geologisches und Paleontologisches Institut und Museum, Christian Albrechts Universität, Olshausenstrasse 40/60, D-971 Kiel, Federal Republic of Germany Search for other works by this author on: GSW Google Scholar J. Paul Dauphin J. Paul Dauphin 6College of Oceanography, Oregon State University, Corvallis, Oregon 97331-5503 Search for other works by this author on: GSW Google Scholar Geology (1986) 14 (3): 199–203. https://doi.org/10.1130/0091-7613(1986)14<199:DOBSAQ>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Margaret Leinen, Douglas Cwienk, G. Ross Heath, Pierre E. Biscaye, V. Kolla, Jørn Thiede, J. Paul Dauphin; Distribution of biogenic silica and quartz in recent deep-sea sediments. Geology 1986;; 14 (3): 199–203. doi: https://doi.org/10.1130/0091-7613(1986)14<199:DOBSAQ>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract All available quartz and biogenic silica concentrations from deep-sea surface sediments were intercalibrated, plotted, and contoured on a calcium-carbonate-free basis. The maps show highest concentrations of biogenic silica (opal) along the west African coast, along equatorial divergences in all oceans, and at the Polar Front in the southern Indian Ocean. These are all areas where upwelling is strong and there is high biological productivity. Quartz in pelagic sediments deposited far from land is generally eolian in origin. Its distribution reflects dominant wind systems in the Pacific, but in much of the Atlantic and Indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A transfer function for estimating paleoceanographic conditions based on deep-sea surface sediment distribution of radiolarian assemblages in the South Atlantic

A quantitative analysis of radiolarian species in 57 deep-sea surface sediment samples from the South Atlantic Ocean produced four geographically distinct assemblages (tropical, polar, gyre margin, and subtropical). The distributions of these assemblages or factors coincide with present-day patterns of sea-surface temperatures or water masses. These four assemblages were used to construct a transfer function relating radiolarian distribution in the surface sediments to present-day winter and summer temperatures using standard regression techniques. As a test of the quality of this transfer function, temperatures were estimated on surface sediment samples from the eastern South Pacific. The temperatures produced by the transfer function compared favorably with the observed (present-day) winter and summer sea-surface temperatures at these sites.

Vertical distribution of polycystine radiolarians in the central North Pacific

Stratified opening/closing net tows in the upper 2000 m of the central North Pacific reveal the major features of the vertical zonation of polycystine radiolarians. Depth profiles of total radiolarian densities show high values at the surface, sharp decrease to a minimum at about 50 m, a maximum exceeding surface levels at about 100 m, and a decrease then to very low values at about 300 m which persist through the rest of the sampled water column. Individual species profiles indicate that the following zones can be identified: (1) A surface zone characterized by a sharp subsurface decrease from high densities at the surface. Densities are an order of magnitude lower by depths of 50–100 m. The rate of decrease resembles the temperature decrease in the thermocline. (2) An upper subsurface maximum zone characterized by species which are absent or very scarce at the surface and reach a pronounced maximum at about 50–100 m. Hydrographic features within the zone are the shallow salinity minimum and the oxygen maximum. A regional chlorophyll maximum occurs at about the same depth as the radiolarian maximum. (3) A lower subsurface maximum zone distinguished from the upper one by occurrence of the maximum about 100 m deeper. Species in this zone are generally scarce at the depth of the upper maximum while species in the upper maximum are scarce at the depth of this maximum. This zone is below the shallow salinity minimum and within the depth of the subjacent salinity maximum which characterizes the habitat of other (tripylean) radiolarians in this area. (4) A deep zone characterized by species which are never abundant but which are consistently absent from the upper few hundred meters. The North Pacific Intermediate Water, previously identified as a tripylean habitat, lies in the depth range of these species, though they may also extend deeper. Despite their lower densities, these species are conspicuous in deep-sea surface sediments.

Cosmic Dust in Recent Deep-Sea Sediments

By means of a simple density-measuring technique, black magnetic cosmic spherules, found in the deep-sea surface sediments, can be divided into two main groups. Further analysis shows the spherules of the first group (density about 3) to be a fine-grained magnesium-rich olivine; and those of the second group (density about 6) to be a partially oxidized nickel + iron alloy. These results strongly indicate a meteoritic origin, and, following Opik 1956, it is suggested that the spherules are derived from the Zodiacal Cloud. The expected amount of zodiacal material accreted to the earth is in fair agreement with direct observation, and it is tempting to regard the cloud as a swarm of small dust flakes produced by the collision of meteoritic (or asteroidal) bodies. Interaction with the upper atmosphere, at speeds near the earth’s escape velocity, would cause some of the larger flakes to melt, and in the case of olivine this would account for its blackened magnetic state. Only the magnetic fraction of the sediments have been examined; it is not known whether other extra-terrestrial material is present in the non-magnetic portion. Over 260 spherules were extracted from two Atlantic samples and one Pacific sample. A very simple method for comparing the recent rates of sedimentation for the various parts of the oceans is suggested. The size distributions of the spherules are discussed in terms of Whipple’s micro-meteorite theory. The minimum size of the iron spherules, occurring at about 15 μ diameter, is used to account for an unexpected depression or ‘forbidden region’ in the stony size distribution near 60 μ . Since the smallest stony spherules found were about 18 μ , it may be suspected that our observations were limited to sizes above about 15 μ . This may be true, as settling-out techniques had to be used in order to rid the sediment of fine magnetite grains, particularly troublesome in the Atlantic samples. However, on occasions the settling process was omitted for the Pacific sediment and careful attention paid to the smaller particles; no spherules below about 15 μ could be found. It is very important to obtain the correct lower limit of the size distributions, and the examination of magnetite-free sediments would be extremely helpful in any future work.