Basalts and serpentinite from the Puerto Rico Trench, 1. Petrology

Typical abyssal tholeiites occur on both north and south walls of the Puerto Rico Trench. Probably they were erupted in the Mid-Atlantic Ridge in Cretaceous time and afterwards were moved to the present position. In addition, doleritic basalts containing phenocrysts of pigeonite rimmed by augite were found from the north wall, and these rocks presumably represent a new type of abyssal tholeiites characterized by $\text{CaO}\text{Na}{}_2\text{O}$ ratios lower than those of ordinary abyssal tholeiites.A new analysis of serpentinite from the north wall is also recorded here.     

A new box corer design for the investigation of manganese-nodule distribution in a sediment column

A new, inexpensive and easy-to-handle box corer (47 × 47 × 114 cm³) is described. It is found to be extremely handy when operated from ships equipped with piston coring devices. The box corer uses the same piston core-head (～1000 kg) and the same trigger mechanism as used in piston coring. The whole operation is similar to that of piston coring. At three sites in the nodule-rich abyssal-hill province in the northwest Atlantic, the vertical distributions of the manganese nodules were obtained from the box cores. More than 75% of the nodules by weight is present in the top 10 cm of the sediment; 16–24% is present in the 10–20 cm interval and about 1% in the 20–30 cm interval. Very few nodules are found below 30 cm.     

Influence of food supply on the δ13C signature of mollusc shells: implications for palaeoenvironmental reconstitutions

Compared to oxygen isotopes, the carbon isotope composition of biogenic carbonates is less commonly used as proxy for palaeoenvironmental reconstructions because shell δ¹³C is derived from both dissolved inorganic (seawater) and organic carbon sources (food), and interactions between these two pools make it difficult to unambiguously identify any independent effect of either. The main purpose of this study was to demonstrate any direct impact of variable food supply on bivalve shell δ¹³C signatures, using low/high rations of a ¹³C-light mixed algal diet fed to 14-month-old (adult) cultured Japanese Crassostrea gigas under otherwise essentially identical in vitro conditions during 3 summer months (May, June and July 2003, seawater temperature means at 16, 18 and 20 °C respectively) in experimental tanks at the Argenton laboratory along the Brittany Atlantic coast of France. At a daily ration of 12% (versus 4%) oyster dry weight, the newly grown part of the shells (hinge region) showed significantly lower δ¹³C values, by 3.5‰ (high ration: mean of −5.8  ± 1.1‰, n = 10; low ration: mean of −2.3  ± 0.7‰, n = 6; ANOVA Scheffe’s test, p < 0.0001). This can be explained by an enhanced metabolic activity at higher food supply, raising ¹³C-depleted respiratory CO₂ in the extrapallial cavity. Based on these δ¹³C values and data extracted from the literature, and assuming no carbon isotope fractionation between food and shell, the proportion of shell metabolic carbon would be 26  ± 7 and 5  ± 5% for the high- and low-ration C. gigas shells respectively; with carbon isotope fractionation (arguably more realistic), the corresponding values would be 69  ± 14 and 24  ± 9%. Both groups of cultured shells exhibited lower δ¹³C values than did wild oysters from Marennes-Ol éron Bay in the study region, which is not inconsistent with an independent influence of diet type. Although there was no significant difference between the two food regimes in terms of δ¹⁸O shell values (means of 0.1  ± 0.3 and 0.4  ± 0.2‰ at high and low rations respectively, non-significant Scheffe’s test), a positive δ¹³C vs. δ¹⁸O relationship recorded at high rations supports the interpretation of a progressive temperature-mediated rise in metabolic activity fuelled by higher food supply (in this case reflecting increased energy investment in reproduction), in terms not only of δ¹³C (metabolic signal) but also of δ¹⁸O (seawater temperature signal). Overall, whole-shell δ¹⁸O trends faithfully recorded summer/winter variations in seawater temperature experienced by the 17-month-old cultured oysters.     

Deep-sea mining of seafloor massive sulfides

The potential emergence of an ocean mining industry to exploit seafloor massive sulfides could present opportunities for oceanographic science to facilitate seafloor mineral development in ways that lessen environmental harms.     

DMSP and DMS dynamics and microzooplankton grazing in the Labrador Sea: application of the dilution technique

We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d⁻¹), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address.     

Analytic signals for multivariate data

Hilbert transformation is a standard tool in univariate signal-processing. It leaves the information content unaffected for, apart from a change of sign, the iterated transform reproduces the original data. As we know from Fourier transforms, such alternative representations of the same information, notwithstanding their theoretical equivalence with the data, can assist powerfully with extracting and interpreting that information. Although the extension to multivariate data is not so obvious for Hilbert as for Fourier transforms, Nabighian gave a treatment of the bivariale situation in 1984. Fueter, some 50 years earlier, had worked on an analogous extension problem, seeking to generalize complex function theory. On comparing these two developments we learn that, although Nabighian's transforms fit naturally into Fueter's theory, they are only one among many alternative possibilities. This paper presents a general theory, of higher dimensional Hilbert transforms and analytic signals, applicable to data of all dimensions less than eight. The change-of-field-direction fillers used in geophysical data processing are shown to arise as special situations.     

True ‘gravitational lens’ effect for cylindrical deflectors

We show that gravitational light deflection is truly equivalent to the optical effect of a prism and a thin diverging lens when the massive deflector has cylindrical symmetry. We then investigate the possibility of cosmological measurements analogous to those proposed by Refsdal in the spherically-symmetric case.This work was partially supported by FINEP, CNPq, and CAPES.     

Monochromatic observations of three nebular objects in the direction of NGC 1714

Using a CCD as detector, we have observed three nebulosities not yet listed in catalogues; they all present a planetary nebula morphology and are situated in the immediate neighbourhood (less than 3 arc min to the East) of NGC 1714. Observations have been made through interference filters centered on the main emission lines of these objects.The observations were made at the E.S.O. in La Silla (Chile).European Southern Observatory, La Silla, Santrago de Chile.