Regional metamorphism of some Dalradian pelites in the Buchan area,N.E. Scotland

Regional metamorphic zones, based on mineral assemblages in pelites, are presented for the Dalradian rocks of Aberdeenshire and Banffshire, in the type area of Buchan metamorphism; electron microprobe analyses of cordierite (C), staurolite (S), chlorite (Chl), biotite (B) and white mica (Ms) are reported for rocks from the classic sections of the Banffshire coast and the valley of the Ythan.A low grade biotite zone, separates two NE-SW trending sets of higher grade zones, in which the sequence s defined by the entry of cordierite, andalusite (A) and (in the west only) staurolite. The zones are characterised by the assemblages (with quartz and muscovite) B-Chl, C-B-Chl, A-C-B and S-A-B.The western sequence contains a transition towards higher pressure, Barrovian type, metamorphism. The isograds arise from continuous reactions affecting rocks of restricted bulk composition (M/FM). With increasing grade, there is a regular trend towards more magnesian ranges of composition for the assemblages C-B-Chl, A-C-B and finally (as P increases in the west), S-A-B. The isograds form when these assemblages intersect the most Fe⁺⁺-rich rock compositions present which occurs in each case when the biotite M/FM=40. A complex of divariant equilibria, derived for the system KFMASH, is used to model the natural reactions.     

Egg extrusion as a kepone-clearance route in the blue crab,Callinectes sapidus

The concentration of Kepone in extruded egg masses and the backfin muscles of the blue crab,Callinectes sapidus, collected from seven stations in the lower James River and lower Chesapeake Bay was determined. Crabs from the lower James River were generally more contaminated than those from the lower Chesapeake Bay. Extruded eggs contain approximately three times more Kepone than backfin muscle. Egg extrusion is concluded to be a major route of Kepone clearance from female blue crabs.     

The measurement of dissolved organic carbon released by phytoplankton

The effects of applied filtration vacuum and incubation time on the release of dissolved organic carbon (DOC) by natural phytoplankton populations dominated by diatoms were examined. The rate of primary production and release of DOC remained reasonably constant during a 5 hour incubation period. The measured release of DOC was found to be quite sensitive to the applied filtration vacuum, ranging from near 2 percent of fixed carbon (neglecting respiration) for gravity-filtered samples to 36 percent for samples filtered at 40 cm Hg vacuum.     

A study of conditions at the inner core boundary of the earth

A study is made of the thermal and compositional conditions which the liquid outer core must satisfy at the inner core boundary, assuming the inner core to be growing by continual solidification of the heavy component of the liquid alloy in the outer core. It is found that the outer core is strongly destabilized by the compositional gradients driven by the separation process associated with the freezing. Further, it is argued that all the freezing necessary for the growth of the solid inner core cannot occur on a flat interface; most of it must occur above the solid boundary in a region labeled the slurry layer.     

Hydrogen and oxygen isotope exchange reactions between clay minerals and water

The extent of hydrogen and oxygen isotope exchange between clay minerals and water has been measured in the temperature range 100–350° for bomb runs of up to almost 2 years. Hydrogen isotope exchange between water and the clays was demonstrable at 100°. Exchange rates were 3–5 times greater for montmorillonite than for kaolinite or illite and this is attributed to the presence of interlayer water in the montmorillonite structure.Negligible oxygen isotope exchange occurred at these low temperatures. The great disparity in D and O¹⁸ exchange rates observed in every experiment demonstrates that hydrogen isotope exchange occurred by a mechanism of proton exchange independent of the slower process of O¹⁸ exchange.At 350° kaolinite reacted to form pyrophyllite and diaspore. This was accompanied by essentially complete D exchange but minor O¹⁸ exchange and implies that intact structural units in the pyrophyllite were inherited from the kaolinite precursor.     

The decay of the mean solar magnetic field

We have analyzed the effects that differential rotation and a hypothetical meridional flow would have on the evolution of the Sun's mean line-of-sight magnetic field as seen from Earth. By winding the large-scale field into strips of alternating positive and negative polarity, differential rotation causes the mean-field amplitude to decay and the mean-field rotation period to acquire the value corresponding to the latitude of the surviving unwound magnetic flux. For a latitudinally broad two-sector initial field such as a horizontal dipole, the decay is rapid for about 5 rotations and slow with a t ^–1/2 dependence thereafter. If a poleward meridional flow is present, it will accelerate the decay by carrying the residual flux to high latitudes where the line-of-sight components are small. The resulting decay is exponential with an e-folding time of 0.75 yr (10 rotations) for an assumed 15 m s^–1 peak meridional flow speed.E.O. Hulburt Center for Space Research.Laboratory for Computational Physics.     

Sedimentological,geomorphological and dynamic context of debris-mantled glaciers,Mount Everest (Sagarmatha) region,Nepal

This paper presents the sediment, landform and dynamic context of four avalanche-fed valley glaciers (Khumbu, Imja, Lhotse and Chukhung) in the Mount Everest (Sagarmatha) region of Nepal. All four glaciers have a mantle of debris dominated by sandy boulder-gravel that suppresses melting to an increasing degree towards the snout, leading to a progressive reduction in the overall slope of their longitudinal profile. Prominent lateral–terminal moraine complexes, also comprising sandy bouldergravel, enclose the glaciers. These terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin, probably by folding and thrusting when the glaciers were more dynamic during the Little Ice Age. The four glaciers are in various stages of recession, and demonstrate a range of scenarios from down-wasting of the glacier tongue, through morainedammed lake development, to post-moraine-dam breaching. Khumbu Glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake, although one is likely to develop behind its >250 m high composite terminal moraine. Imja Glacier terminates in a substantial body of water behind a partially ice-cored moraine dam (as determined from geophysical surveys), but morphologically appears unlikely to be an immediate threat. Chukhung Glacier already has a breached moraine and a connected debris fan, and therefore no longer poses a threat. Lhotse Glacier has an inclined, free-draining tongue that precludes hazardous lake development. From the data assembled, a conceptual model, applicable to other Himalayan glaciers, is proposed to explain the development of large, lateral-terminal moraine complexes and associated potentially hazardous moraine dams. – 2008 Elsevier Ltd. All rights reserved.     

The origin of the 28- to 29-day recurrent patterns of the solar magnetic field

Numerical simulations of the Sun's mean line-of-sight magnetic field suggest an origin for the 28-to 29-day recurrent patterns of the field and its associated interplanetary phenomena. The patterns are caused by longitudinal fluctuations in the eruption of new magnetic flux, the transport of this flux to mid latitudes by supergranular diffusion and meridional flow, and the slow rotation of the resulting flux distributions at the 28- to 29-day periods characteristic of those latitudes.E. O. Hulburt Center for Space Research.Laboratory for Computational Physics.     

The use of land recorded long-range marine airgun data in crustal reflection-refraction investigations

Summary. During the EUGENO-S field campaign in 1984 a large number of airgun shots were fired at sea in the Skagerrak and Kattegat and in Lake Vänern in southwestern Sweden. The signals were recorded on land by analogue "MARS" and digital "SN-PCM-80" three channel stations, by a digital 48 channel "SERCEL SN348" reflection instrument, and by "Geostore" stations. The airguns were shot about every 300 m along profiles up to 100 km in length. Clear reflected and refracted arrivals were observed from 5 km to 250 km shot-receiver offset. The field and data processing techniques used are briefly described, and two examples of data are discussed.