Annotated record of the detailed examination of Mn deposits from R/V Atlantis - Cruise 151 (Dec. 1947) in the Atlantic Ocean

One of the objectives of WHOI Atlantis Cruise 151, covering the period from 7 December 1947 to 18 June 1948, was to obtain as complete a sampling of the sea bottom of the Meditterranean and Aegean Seas as was compatible with the remainder of the scientific program. It was furthermore planned to make concurrent bottom photographs as a means for studying the correlation between bottom sediments and the morphology of the sea floor. The photographs also held the possibility of determining the presence of bottom fauna. The underwater camera used for this work was loaned to us by Dr. Maurice Ewing of Columbia University. As it was fitted with a one foot long coring tube at the base of its pole a majority of the bottom samples were obtained by the camera itself. On the way to Gibraltar, several bottom photos were taken in the Atlantic ocean. One of them was the deepest underwater photograph ever taken at the tima (3026 fathoms) showing a cluster of objects, some as much as 5 inches across on a clay bottom. These appeared to be manganese nodules, judging from their rounded and bulbous shape, especially the potato-like form of some of them. A core sample obtained at the same spot with a corer attached to the camera stand contained abundant manganese grains.

Particle size of Saharan dust in the Atlantic Ocean, from October 2012 to November 2013

Mineral dust has a large impact on regional and global climate, depending on its particle size. Especially in the Atlantic Ocean downwind of the Sahara, the largest dust source on earth, the effects can be substantial but are poorly understood. This study focuses on seasonal and spatial variations in particle size of Saharan dust deposition across the Atlantic Ocean, using an array of submarine sediment traps moored along a transect at 12° N. We show that the particle size decreases downwind with increased distance from the Saharan source, due to higher gravitational settling velocities of coarse particles in the atmosphere. Modal grain sizes vary between 4 and 33 µm throughout the different seasons and at five locations along the transect. This is much coarser than previously suggested and incorporated into climate models. In addition, seasonal changes are prominent, with coarser dust in summer, and finer dust in winter and spring. Such seasonal changes are caused by transport at higher altitudes and at greater wind velocities during summer than in winter. Also the latitudinal migration of the dust cloud, associated with the Intertropical Convergence Zone, causes seasonal differences in deposition as the summer dust cloud is located more to the north, and more directly above the sampled transect. Furthermore, increased precipitation and more frequent dust storms in summer coincide with coarser dust deposition. Our findings contribute to understanding Saharan dust transport and deposition relevant for the interpretation of sedimentary records for climate reconstructions, as well as for global and regional models for improved prediction of future climate.

Annotated record of the detailed examination of Mn deposits in the Atlantic Ocean from cruises from R/V Atlantis II, R/V Knorr, R/V Melvin and R/V James M. Gilliss in 1980-1981

This report is Volume 3 of Descriptions of WHOI rock dredge samples. This series represents a major effort to catalog the rock dredge samples in the WHOI Sea Floor samples collection, and to disseminate this information throughout the scientific community. Volume 3 contains sample descriptions and station data for the dredge stations from five cruises during the period September 1978 through December 1980. The material in this and subsequent volumes of rock descriptions was largely prepared onboard ship by the participating scientists. Volume 3 was printed prior to volumes 1 and 2 because of the excellent documentation of the samples represented in this volume.

Observation of manganese nodules and crusts recovered during the CHAIN 115 cruise from Nov 1973 until June 1974 in the Atlantic Ocean

Investigations of piston cores from the Vema Channel and lower flanks of the Rio Grande Rise suggest the presence of episodic flow of deep and bottom water during the Late Pleistocene. Cores from below the present-day foraminiferal lysocline (at ~4000 m) contain an incomplete depositional record consisting of Mn nodules and encrustations, hemipelagic clay, displaced high-latitude diatoms, and poorly preserved heterogeneous microfossil assemblages. Cores from the depth range between 2900 m and 4000 m contain an essentially complete Late Pleistocene record, and consist of well-defined carbonate dissolution cycles with periodicities of ~100,000 years. Low carbonate content and increased dissolution correspond to glacial episodes, as interpreted by oxygen isotopic analysis of bulk foraminiferal assemblages. The absence of diagnostic high-latitude indicators (Antarctic diatoms) within the dissolution cyclss, however, suggests that AABW may not have extended to significantly shallower elevations on the lower flanks of the Rio Grande Rise during the Late Pleistocene. Therefore episodic AABW flow may not necessarily be the mechanism responsible for producing these cyclic events. This interpretation is also supported by the presence of an apparently complete Brunhes depositional record in the same cores, suggesting current velocities insufficient for significant erosion. Fluctuations in the properties and flow characteristics of another water mass, such as NADW, may be involved. The geologic evidence in core-top samples near the present-day AABW/NADW transition zone is consistent with either of two possible interpretations of the upper limit of AABW on the east flank of the channel. The foraminiferal lysocline, at ~4000 m, is near the top of the benthic thermocline and nepheloid layer, and may therefore correspond to the upper limit of relatively corrosive AABW. On the other hand, the carbonate compensation depth (CDD) at ~4250 m, which corresponds to the maximum gradient in the benthic thermocline, is characterized by rapid deposition of relatively fine-grained sediment. Such a zone of convergence and preferential sediment accumulation would be expected near the level of no motion in the AABW/NADW transition zone as a consequence of Ekman-layer veering of the mean velocity vector in the bottom boundary layer. It is possible that both of these interpretations are in part correct. The "level of no motion'' may in fact correspond to the CCD, while at the same time relatively corrosive water of Antarctic origin may mix with overlying NADW and therefore elevate the foraminifera] lysocline to depths above the level of no motion. Closely spaced observations of the hydrography and flow characteristics within the benthic thermocline will be required in order to use sediment parameters as more precise indicators of paleo-circulation.

Annotated record of the detailed examination of Mn deposits from various ship expeditions in the Atlantic Ocean from 1876 until 1911

The greater part of this Monograph is devoted to detailed descriptions of 1426 samples of deposits from the floor of the Atlantic Ocean stored in the Challenger Office, Edinburgh, which had been collected during thirty-five cruising expeditions between 1857 and 1911. The remaining part discusses the results of the work. The work of examining and describing in detail this abundant mass of material was in progress when the late Sir JOHN MURRAY met his death in March 1914. By that time about three-fourths of the descriptive work had been completed under his supervision. Sir John's trustees arranged for the completion of the descriptive work by Mr Chumley, and this was done in the Challenger Office during the two succeeding years. Later, after he had removed to Glasgow, Mr Chumley prepared the notes discussing the results. The trustees have pleasure in recording, on the suggestion of Mr Chumley, the courtesy of Dr G. W. Lee of the Geological Survey of Scotland, for help in determining many of the rarer mineral particles contained in the deposits.