C4-C7 alkenones in deep sea sediments

It is believed that C4 to C7 hydrocarbons in petroleum are formed by the cracking of organic matter at depths generally exceeding 1,000 m at temperatures in excess of 50 °C (Cordel, 1972; Dow, 1974; Tissot et al., 1974)). Also, none of the alkanes in the butane-heptane range are formed biologically as far as is known at present. Consequently, it is thought that they do not occur in shallow, Recent sediments. In 1962, I analysed 22 samples of Recent sediments from 7 different environments and verified that these hydrocarbons were not present at the p.p.m. level (Dunton and Hunt, 1962) although traces of a few hydrocarbons such as butane, isobutane, isopentane and n-heptane have been found (Sokolov, 1957; Veber and Turkeltaub, 1958; Erdman et al., 1958; Emery and Hoggan, 1958). No identification of individual hexanes or heptanes has been reported except when there has been clear evidence of seepage from deeper source sediments (McIver, 1973).

Helium isotope ratios and pore gases in deep-sea sediments of the Japan Sea

We have measured the 3He/4He and 4He/20Ne ratios and chemical compositions of gases exsolved from deep-sea sediments at two sites (798 and 799) in the Japan Sea. The 3He/4He and 4He/20Ne ratios vary from 0.642 Ratm (where Ratm is the atmospheric 3He/4He ratio of 1.393*10**-6) to 0.840 Ratm, and from 0.41 to 4.5, respectively. Helium in the samples can be explained by the mixing between atmospheric helium dissolved in bottom water of the Japan Sea and crustal helium in the sediment. The sedimentary helium is enriched in mantle-derived 3He compared with those from the Japan Trench and the Nankai Trough. This suggests that the basement of the Japan Sea has relatively large remnants of mantle-derived helium compared with that of the Pacific. Major chemical compositions of the samples are methane and nitrogen. There is a positive correlation between methane content and helium content corrected for air component. Based on the 3He/4He-Sum C/3He diagram, the major part of methane can be attributed to crustal and/or organic origin.

Late Eocene to Recent deep-sea benthic foraminifera from the Central equatorial Pacific Ocean

Benthic foraminifers were studied in upper Eocene to Recent core-catcher samples from DSDP Sites 573, 574, and 575. The sites are on a north-south transect from the equator to about 05°N at about 133°W, water depth 4300 to 4600 m. At Site 574 additional samples were used to study the Eocene/Oligocene boundary in detail. About 200 specimens were counted per sample. The fauna is highly diverse (about 50 to 70 species per sample) and is of low dominance. The diversity is not related to age or sub-bottom depth. Many species are cosmopolitan and probably have wide environmental tolerances. Fluctuations in frequency of some taxa (e.g., Nuttallides umbonifera, Epistominella exigua, and Uvigerina spp.) cannot be correlated from one site to another. Several common species (e.g. Oridorsalis umbonatus and Globocassidulina subglobosa) range from late Eocene to Recent. First and last appearances are generally difficult to define precisely because many species are rare. For some species these datums differ from one site to another, but several datum levels are within 1 m.y. at all sites. First and last appearances are most numerous in two intervals, the late Eocene to early Oligocene (about 32 to 37 Ma) and the early to middle Miocene (about 13 to 18.5 Ma). Isotopic events occur within each of these periods of benthic faunal change, but the isotopic events have a shorter duration and start after the initiation of the changes in the fauna. Changes in deep-sea benthic faunal composition are not directly related to short-term oceanographic changes as expressed in isotopic records.

Distribution of deep-sea meiobenthos in surface sediments off North Carolina

Observations on the ecology and distribution of meiofauna occurring on the outer continental shelf and continental slope at depths from 50 to 2500 m in the region where the Blake Plateau cuts across the North Carolina slope are reported. Total numbers of meiofauna ranged from 151/100 cm**3 of sediment at 400 m to 1196/100 cm**3 of sediment at 250 m. Sediments of the upper region (50-500 m) consisted of medium-sized calcareous sands with relatively low organic carbon contents, while the deeper sediments (600-2500 m) consisted of sandy silts and silts with organic carbon contents 6-10 times that of the shallower sediments. Two basic faunas appear to be present in the areas investigated; a shallow-water fauna extending from 50 to 500 m and a deep-water fauna from 800 to 2500 m. The shallow-water fauna consists of nematodes (the dominant taxon) and relatively large numbers of harpactacoid copepods, ostracods, benthic foraminifera, polychaetes, gastrotrichs and several other groups, while below 500 m only nematodes and foraminifera are present in large numbers, the latter being especially abundant between 800 and 2000 m. A major change in the meiofauna occurs on the Blake Plateau between the depths of approximately 400-500 m and 600-750 m where the composition of the sediment changes from sand to silty sand. From 50 m to 400-500 m gastrotrichs, turbellaria, tardigrades, kinorhynchs, halicarids, hydrozoans, gnathostomulids, lamellibranchs and cumaceans are commonly encountered; these groups are absent below 500 m. In addition, there are significant reductions in the numbers of harpactacoids, ostracods, nemerteans and polychaetes below 500 m. Examination of the nematode population also show faunal differences between the shallower sediments (50-500 m) and the deeper sediments (600-2500 m). High indices of affinity exist among the faunas between 50 and 500 m and among the faunas between 800 and 2500 m; the fauna at 600-750 m represents a transition between these two regions, but it is more closely related to the deep-water fauna. Changes in the distribution of both the total meiofuna and also the nematodes are highly correlated with changes in sediments composition and bottom water temperatures. It is suggested that changes in grain size and accompanying changes in sources of nutrition, which are the results of Gulf Stream and other current activity, are the dominant environmental factors influencing the meiofauna of the area.

Biogenic opal estimation of deep-sea sediment cores from the Scotia Sea

We present biogenic opal flux records from two deep-sea sites in the Scotia Sea (MD07-3133 and MD07-3134) at decadal-scale resolution, covering the last glacial cycle. Besides conventional and time-consuming biogenic opal measuring methods, we introduce new biogenic opal estimation methods derived from sediment colour b*, wet bulk density, Si/Ti-count ratio, and Fourier transform infrared spectroscopy (FTIRS). All methods capture the biogenic opal amplitude, however, FTIRS - a novel method for marine sediment - yields the most reliable results. 230Th normalization data show strong differences in sediment focusing with intensified sediment focusing during glacial times. At MD07-3134 230Th normalized biogenic opal fluxes vary between 0.2 and 2.5 g/cm2/kyr. Our biogenic opal flux records indicate bioproductivity changes in the Southern Ocean, strongly influenced by sea ice distribution and also summer sea surface temperature changes. South of the Antarctic Polar Front, lowest bioproductivity occurred during the Last Glacial Maximum when upwelling of mid-depth water was reduced and sea ice cover intensified. Around 17 ka, bioproductivity increased abruptly, corresponding to rising atmospheric CO2 contents and decreasing seasonal sea ice coverage.

Deep sea searches : the story of the seabed assessment program.

Mode of access: Internet.

Deep sea exploration in Faeroe Channel by H.M.S. "Triton", 1882 /

Mode of access: Internet.

Among the deep sea fishers.

Description based on: July 1909; title from cover.

Oceanic ichthyology, a treatise on the deep-sea and pelagic fishes of the world, based chiefly upon the collections made by the steamers Blake, Albatross, and Fish Hawk in the northwestern Atlantic, with an atlas containing 417 figures.

Published at the joint expense of the Smithsonian institution and the United States National museum.

Deep-sea plunderings; a collection of stories of the sea,

Mode of access: Internet.

High-resolution cyclostratigraphy of the Cenomanian-Turonian interval: Paleoceanographic implications, a comparison between deep sea drilling project site 386 and 144

The purpose of this study was to determine the extent to which oceanic anoxic events (OAE's) are recorded in deep-water deposits of the former western Tethyan Sea, by investigating the Cenomanian-Turonian time interval characterized by the worldwide OAE 2 event. The study improved our knowledge of the possible controlling mechanisms that triggered this event at these sites, and furthered our understanding of this global phenomenon. This was examined by high-resolution, multi-proxy analyses of sediments at DSDP Sites 386 and 144, including sedimentology, scanning electron microscopy, stable isotopes, bulk and clay mineralogy, major and trace element geochemistry, biomarkers, and paleontological data. ^ The results provide a better stratigraphic resolution for the Cenomanian-Turonian, which allowed for more precise determination of chronologic boundaries, sedimentation rates at DSDP Site 386, and a more accurate calculation of the frequency of the cycles recorded in the sequence, which fall predominantly within the precession (∼23 kyr) and short eccentricity (∼100 kyr) ranges. The combined proxies allow assessment of the correlation of δ13Corg, and major and trace elements with the predominance of cyanobacteria. These organisms were the main producers of the organic matter during the dysoxic and euxinic conditions of OAE 2 at DSDP Site 386. A huge amount of microcrystalline quartz of eolian origin is also associated with OAE 2. The geochemical proxies further provide evidence that OAE 2 was linked to increased volcanism outside the deep water of the proto-Atlantic Ocean. The clays in the Turonian sediments are terrigenous and derived predominantly from eolian transport. Comparing DSDP Site 386 and 144 with stratotype sections, the δ13C org and TOC data indicate that OAE 2 seems diachronous throughout the proto-Atlantic Ocean. ^ This study concludes that the development of anoxic conditions in the deep water of the Atlantic during the latest Cenomanian-Turonian resulted from a combination of factors related to local oceanic setting and mitigated by global tectonism and climate. The data provide a more comprehensive view of the interacting factors that led to sustained high productivity of the cyanobacteria and photosynthetic protists that produced organic-carbon-rich deposits in the world's oceans. ^

Results of an isotope tracer experiment with arctic deep-sea nematodes

A stable isotope (13C)-labeling experiment was performed to quantify the importance of bacterial carbon as a food source for an Arctic deep-sea nematode community. Bacterial functional groups were isotopically enriched with 13C-glucose, 13C-acetate, 13C- bicarbonate, and 13C-amino acids injected into sediments collected from 1280 m depth at 79uN, 6uE, west of Svalbard. Incorporation of the 13C label into bacterial phospholipid-derived fatty acids (PLFAs) and nematodes in the top 5 cm of the sediment was monitored over a 7-d period. The 13C dynamics of nematodes was fitted with a simple isotope turnover model to derive the importance of the different bacterial functional groups as carbon sources for the nematodes. The different substrates clearly labeled different bacterial groups as evidenced by differential labeling of the PLFA patterns. The deep-sea nematode community incorporated a very limited amount of the label, and the isotope turnover model showed that the dynamics of the isotope transfer could not be attributed to bacterivory. The low enrichment of nematodes suggests a limited passive uptake of injected 13C-labeled substrates. The lack of accumulation suggests that the injected 13C-labeled dissolved organic carbon compounds are not important as carbon sources for deep-sea nematodes. Since earlier studies with isotopically enriched algae also found limited uptake by nematodes, the food sources of deep-sea nematodes remain unclear.