Shell preservation of Limacina inflata in surface sediments of the Central and South Atlantic

Over 300 surface sediment samples from the Central and South Atlantic Ocean and the Caribbean Sea were investigated for the preservation state of the aragonitic test of Limacina inflata. Results are displayed in spatial distribution maps and are plotted against cross-sections of vertical water mass configurations, illustrating the relationship between preservation state, saturation state of the overlying waters, and overall water mass distribution. The microscopic investigation of L. inflata (adults) yielded the Limacina dissolution index (LDX), and revealed three regional dissolution patterns. In the western Atlantic Ocean, sedimentary preservation states correspond to saturation states in the overlying waters. Poor preservation is found within intermediate water masses of southern origin (i.e. Antarctic intermediate water (AAIW), upper circumpolar water (UCDW)), which are distinctly aragonite-corrosive, whereas good preservation is observed within the surface waters above and within the upper North Atlantic deep water (UNADW) beneath the AAIW. In the eastern Atlantic Ocean, in particular along the African continental margin, the LDX fails in most cases (i.e. less than 10 tests of L. inflata per sample were found). This is most probably due to extensive "metabolic" aragonite dissolution at the sediment-water interface combined with a reduced abundance of L. inflata in the surface waters. In the Caribbean Sea, a more complex preservation pattern is observed because of the interaction between different water masses, which invade the Caribbean basins through several channels, and varying input of bank-derived fine aragonite and magnesian calcite material. The solubility of aragonite increases with increasing pressure, but aragonite dissolution in the sediments does not simply increase with water depth. Worse preservation is found in intermediate water depths following an S-shaped curve. As a result, two aragonite lysoclines are observed, one above the other. In four depth transects, we show that the western Atlantic and Caribbean LDX records resemble surficial calcium carbonate data and delta13C and carbonate ion concentration profiles in the water column. Moreover, preservation of L. inflata within AAIW and UCDW improves significantly to the north, whereas carbonate corrosiveness diminishes due to increased mixing of AAIW and UNADW. The close relationship between LDX values and aragonite contents in the sediments shows much promise for the quantification of the aragonite loss under the influence of different water masses. LDX failure and uncertainties may be attributed to (1) aragonite dissolution due to bottom water corrosiveness, (2) aragonite dissolution due to additional CO2 release into the bottom water by the degradation of organic matter based on an enhanced supply of organic matter into the sediment, (3) variations in the distribution of L. inflata and hence a lack of supply into the sediment, (4) dilution of the sediments and hence a lack of tests of L. inflata, or (5) redeposition of sediment particles.

Grain size distribution analysis of prominent beds on Southern Central Chilean seamounts

Gravity cores obtained from isolated seamounts located within, and rising up to 300 m from the sediment-filled Peru-Chile Trench off Southern Central Chile (36°S-39°S) contain numerous turbidite layers which are much coarser than the hemipelagic background sedimentation. The mineralogical composition of some of the beds indicates a mixed origin from various source terrains while the faunal assemblage of benthic foraminifera in one of the turbidite layers shows a mixed origin from upper shelfal to middle-lower bathyal depths which could indicate a multi-source origin and therefore indicate an earthquake triggering of the causing turbidity currents. The bathymetric setting and the grain size distribution of the sampled layers, together with swath echosounder and sediment echosounder data which monitor the distribution of turbidites on the elevated Nazca Plate allow some estimates on the flow direction, flow velocity and height of the causing turbidity currents. We discuss two alternative models of deposition, both of which imply high (175-450 m) turbidity currents and we suggest a channelized transport process as the general mode of turbidite deposition. Whether these turbidites are suspension fallout products of thick turbiditic flows or bedload deposits from sheet-like turbidity currents overwhelming elevated structures cannot be decided upon using our sedimentological data, but the specific morphology of the seamounts rather argues for the first option. Oxygen isotope stratigraphy of one of the cores indicates that the turbiditic sequences were deposited during the last Glacial period and during the following transition period and turbiditic deposition stopped during the Holocene. This climatic coupling seems to be dominant, while the occurrence of megathrust earthquakes provides a trigger mechanism. This seismic triggering takes effect only during times of very high sediment supply to the shelf and slope.

Sludge dewatering and drying on sand beds /

Mode of access: Internet.

Drag on naturally rippled beds under oscillatory flows /

Includes abstract.

Elementary theory of nuclear shell structure /

Mode of access: Internet.

Stresses in aircraft and shell structures.

James P. Peterson was closely associated with a large part of the work.

Flow of gases through beds of broken solids,

At head of title: United States Department of commerce. R.P. Lamont, secretary. Bureau of Mines. Scott Turner, director.

The Shell (Conus marmoreus), 2nd state

Rembrandt van Rijn; 3 13/16 in.x 5 5/32 in.; etching and drypoint on paper

The talking budgie (Australian shell parrakeet)

Mode of access: Internet.

Handbook for shell collectors; illustrations and descriptions of shells from all parts of the world.

Mode of access: Internet.

A catalogue of surgeons' instruments, air and water beds, pillows, and cushions, bandages, trusses... : manufactured and sold by S. Maw & son.

Mode of access: Internet.

A Scallop shell of quiet,/

Reprinted in part from various periodicals.

Bibliography on shell molding.

Mode of access: Internet.

Higher shell corrections in stopping power /

"Prepared under the auspices of the Atomic Energy Commission Contract AT(04-3)-136."

The chick book, from the breeding pen through the shell to maturity : contains the experience of the world's leading poultrymen and all the latest and most trustworthy information about hatching, rearing, fattening and marketing chickens.

Mode of access: Internet.