An Active Sun Throughout the Maunder Minimum

Measurements of ¹⁰Be concentration in the Dye 3 ice core show that magnetic cycles persisted throughout the Maunder Minimum, although the Sun's overall activity was drastically reduced and sunspots virtually disappeared. Thus the dates of maxima and minima can now be reliably estimated. Similar behaviour is shown by a nonlinear dynamo model, which predicts that, after a grand minimum, the Sun's toroidal field may switch from being antisymmetric to being symmetric about the equator. The presence of cyclic activity during the Maunder Minimum limits estimates of the solar contribution to climatic change.     

Towards Asteroseismology from Space, the EVRIS experiment. Opto-mechanical characteristics and pointing performances of the EVRIS/PAIS complex

EVRIS is the first space experiment dedicated to asteroseismology. It is designed to measure the relative time variations of the flux of several bright stars and to detect their modes of pulsation. As the amplitudes of these oscillations should be very small (a few ppm), the instrument has to perform relative photometry with an extremely high accuracy, i.e. hundred times better than the classical accuracy reached from the ground. The experiment is composed of a star tracker and a photometer, mounted on a pointing platform PAIS. This paper describes the mechanical and optical design and the performance of EVRIS, as well as the properties of the pointing system. It is shown that the EVRIS/PAIS complex meets the scientific specifications for a list of targets well suited for asteroseismology. The EVRIS collaboration is composed of: G. Epstein, J.P. Michel, F. Rakotoarivelo, F. Roubaud and A. Mangeney Observatoire de Paris (DESPA) 92195 Meudon, FranceA. Magnan, J.C. DavidLaboratoire d'Astronomie Spatiale, BP8 - Traverse du Siphon, 13012 Marseille, FranceJ.T. BueyObservatoire de Paris (DESPA) 92195 Meudon, FranceObservatoire de Paris (DASGAL) 92195 Meudon, FranceR. BellengerDépartement d'Astrophysique Extragalactique et de Cosmologie, Observatoire de Paris, FranceM. Gelbmann, U. Heiter, F. Hiesberger, R. Kuschnig and E. PaunzenInstitut für Astronomie, Wien Austria     

Early lunar differentiation: 4.42-AE-old plagioclase clasts in Apollo 16 breccia 67435

We report on a⁴⁰Ar-³⁹Ar study of the Apollo 16 breccia 67435 and present ages of five samples representing matrix, lithic clasts and plagioclase clasts. While the matrix age spectrum does not have a well-defined plateau, the two lithic clasts gave plateau ages of 3.96 and 4.04 AE. Since all samples had apparent ages of ～1 AE in the fractions ≤600°C extraction temperature, the breccia might have been assembled in a rather mild process at about that time or even more recently out of material with different metamorphic ages. The two plagioclase samples, of which one was a single 9-mg mineral clast and the other a 15-mg composite of several clasts, also have ages of ～1 AE in the low-temperature release fractions, but are apparently undisturbed by any ～4-AE events since they both have well-defined plateaux at 4.42 AE. The age of these strongly calcic plagioclase clasts, believed to be remnants of the anorthositic lunar crust, establishes a lower age limit to the end of the early lunar differentiation and thus places a strong constraint to the lunar evolution.     

Chemistry of submarine hydrothermal solutions at 21 °N,East Pacific Rise

The three hydrothermal fields at 21°N latitude, East Pacific Rise, were resampled and an additional one was discovered. Maximum fluid temperatures observed were within a few degrees of 350°C and these waters had concentrations of Mg and sulfate indistinguishable from zero. One field, NGS, which had active 350°C springs in 1979, was inactive when first located in 1981. However, when a chimney was broken open during sampling, water issued at 273°C and continued to flow for at least five days. The chemical composition strongly suggests that these waters cooled conductively from 350°C in the sealed conduit.The major ion data are consistent with the estimates based on extrapolation of the original measurements made on the hot springs from the Galapagos Spreading Center (Edmondet al., 1979a). The fluids have a pH of 3.5 and the sulfide-forming element concentrations show significant inter-field variations. Fe levels range from 0.8 to 2.4 mmoles/kg; the ratio Fe:Mn varies from 0.9 to 2.9 similar to metalliferous sediments on the ridge flanks, but much higher than observed at Galapagos (where sub-surface precipitation of iron sulfides occurs) indicating that the overwhelming proportion of the mass flux from hydrothermal systems occurs at high temperatures. Zn ranges from 40 to 106 μmoles/kg with Cu being substantially lower. Since the ratio of these elements in tholeiites is about unity, there is strong net preferential mobilization of Zn. Lead ranges from 183 to 359 nmoles/kg. Nickel and Be are highly immobile relative to the other trace elements. The abundance of H₂S is about three times that of the total sulfide-forming cations. These data demonstrate that acid solutions at elevated temperatures can transport substantial amounts of ore-forming elements in the presence of large excesses of sulfide.     

Helium-3 and manganese at the 21°N East Pacific Rise hydrothermal site

Water samples collected at the 21°N hydrothermal site on the East Pacific Rise crest, including Deep-Tow and hydrocast samples collected in 1977 and three hot vent water samples collected recently with the submersible “Alvin”, contain significant additions of³He,⁴He, and Mn. Although the vent water collections were at least 50-fold diluted with ambient seawater, they are up to 53 times enriched in³He and 7.4 times enriched in⁴He relative to saturated seawater, with concentrations of total dissolvable manganese (TDM) up to 310 μg/kg.³He and⁴He covary in the vent samples, with³He/⁴He about 8 times the atmospheric ratio, reflecting a mantle helium source. In contrast to the helium isotopes the Mn/³He ratio in the vent samples is variable, ranging from 4.3 × 10⁴ up to 1.0 × 10⁵ g/cm³. Profiles of³He/⁴He and TDM in the water column at 21°N show a sharp maximum ofδ(³He) = 47%and TDM= 0.69 μg/kg, much higher than the average values of 34% and 0.2 μg/kg for the deep water in this region. This spike in³He and Mn occurs at 2400 m depth, 200 m above the level of the 21°N vents, and 100 m higher than any local bathymetry, evidence for upward transport of the hydrothermal discharge via rising plumes of hot vent water. Two of the 21°N Deep-Tow samples associated with small (?0.010°C) temperature anomalies hadδ(³He) = 38%and TDM= 0.28 and 0.58 μg/kg, also slightly elevated relative to background. The Deep-Tow and hydrocast samples have lower Mn/³He ratios than average vent samples due to Mn removal by scavenging. Comparison of vent samples and water column measurements at 21°N indicate that the pure vent water could be detected using³He and Mn even when diluted ～10⁵ times with seawater, confirming that these two tracers are extremely sensitive indicators of submarine hydrothermal activity.     

The relationship between principal stress directions and the geometry of kinks in foliated rocks

This paper describes the results of a series of experiments carried out on card decks and foliated rock in order to study the nucleation and growth of kinks. Parameters varied in the experiments were confining pressure and the angle of inclination between the foliation and the direction of maximum shortening.The results showed that most kinks initiated as symmetric or monoclinal buckles which rapidly changed to an angular, stable form similar to that observed in nature. The amount of strain required to set up this stable geometry is small. The effect of increasing confining pressure is to diminish the size of the kinks while that of changing the angle of inclination of the foliation to the direction of maximum shortening is to modify the style of deformation from the development of a set of conjugate kinks at small angles (0 – 5°), to a single set of kinks at larger angles (5 – 15°), and, finally, to a combination of sliding along the foliation and kinking at the largest angles (15 – 30°) investigated.During this change in mode of deformation, the angular relationships between the kinks and the directions of the applied loads change systematically and graphs are presented which may be of use in relating the geometry of natural kinks to the principal stress directions.     

Climate change,intergenerational equity and international law: An introductory note

The change in the Earth's climate caused by the accumulation of greenhouse gases in the atmosphere may be the most important environmental legacy that we leave to our descendants.Global change raises difficult issues of equity between our generation and future generations, and between different communities within future generations. International law is accustomed to addressing the effects of intentional environmental change on people who are already alive. It needs to be augmented by principles of intergenerational equity. We have certain obligations to future generations to pass on a planet in no worse condition than we received it and to give them equitable access to its resources.This requires a global strategy for climate change which will prevent excessively rapid climate change, prevent or mitigate the damage caused by climate change, and help countries to adapt to climate change. We need to avoid imposing major costs on future generations for our own benefit.To implement this strategy will require enforceable norms of behavior, which should be embodied in a Declaration of Planetary Rights and Obligations to Future Generations, and implemented in appropriate treaties and national and local legislation. Agreements should be drafted in such a way that they can incorporate increases in scientific understanding, for example by the creation of scientific advisory committees.     

The Fate of Chernobyl137Cs in Lake Lugano

A rapid removal of Chernobyl¹³⁷Cs from a number of large lakes has been previously reported. Our measurements of¹³⁷Cs in water, sediments and pore water in the mono- and meromictic basins of Lake Lugano (Lago di Lugano) reveal generally slower half-removal times of 1.2 and 6.7 yrs, respectively. In the seasonally anoxic southern basin, this is most probably related to an intensive recycling of¹³⁷Cs between water and sediments. In the permanently stratified northern basin the removal rate is much slower due to an important inventory build up in the deep anoxic part of the basin.     

The speleothem record of climate variability in Southern Arabia

Uranium-series dated stalagmites from Oman indicate that pluvial conditions prevailed from 6.3 to 10.5, 78 to 82, 120 to 130, 180 to 200 and 300 to 330 kyr B.P.; all of these periods coincide with peak interglacials. Oxygen (δ¹⁸O) and hydrogen (δD) isotope ratios of speleothem calcite and fluid inclusions reveal the source of moisture and provide information on the amount of precipitation, respectively. δ¹⁸O and δD values of stalagmites deposited during peak interglacials vary between ?8 and ?4 ‰ (VPDB) and ?53 and ?20‰ (Vienna Standard Mean Ocean Water [VSMOW]) respectively, whereas modern stalagmites range from ?2.6 to ?1.1‰ in δ¹⁸O (VPDB) and ?7.6 and ?3.3‰ in δD (VSMOW), respectively. The growth and isotopic records indicate that during peak interglacial periods, the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coinciding with an interglacial stage of the marine oxygen isotope record.