‘Trapped sea-water’ in Rørholtfjorden

Summary Trapped sea-water in R?rholtfjorden, Telemark, Norway, was discovered in 1951 by?smund Ystad who was a student at the Department of Limnology, University of Oslo. The lake was investigated continuously from August 1951 to July 1952, and the results are found inYstad [12] andStr?m [8, 9, 10, 11]. On 25 February 1971 some water samples were taken from R?rholtfjorden to supply the information from the lake, and if possible record changes in the water for the last 20 years. The tables contain chemical data, pH, temperature and oxygen content. The trapped sea-water is also compared with original sea-water with the same chloride content. It is difficult to say anything about changes in the salt-water because of uncertainty regarding the depth measurements. But a so-called semi-stagnation (Str?m [8]) was not observed (Fig. 3). It is possible that about one meter of the trapped sea-water has been lost during the last 20 years because of the removed semi-stagnation.

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Zusammenfassung Im R?rholtfjord, Telemark, Norwegen, wurde 1951 von?smund Ystad, Universit?t Oslo, ?gefangenes? Meerwasser entdeckt, welches dann von August 1951 bis Juli 1952 kontinuierlich untersucht wurde. Die Resultate sind beiYstad [12] undStr?m [8, 9, 10, 11] publiziert. Im February 1971 wurden erneut Proben aus dem Fjord genommen, um eventuelle Ver?nderungen w?hrend der vergangenen 20 Jahre festzustellen. Es wurden chemische Daten sowie pH, Temperatur und O₂-Gehalt aufgenommen. Das ?gefangene? Wasser wurde auch mit Originalmeerwasser derselben Salinit?t verglichen. Wegen der Ungenauigkeit der Tiefenmessungen ist es schwierig, etwas über Ver?nderungen auszusagen. Indessen wurde eine sog. Semi-Stagnation, wie sieStr?m [8] beschreibt, nicht beobachtet (Fig. 3). M?glicherweise ging etwa 1 m des ?gefangenen? Wassers zufolge des Verschwindens jener Semi-Stagnation verloren.

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Résumé De l’eau de mer ?captivée? dans le R?rholtfjord, Telemark, Norvège, fut découverte en 1951 par?smund Ystad, étudiant en Limnologie à l’Université d’Oslo. Des expériences avec l’eau de ce lac ont été poursuivies continuellement d’ao?t 1951 à juillet 1952 et les résultats ont été publiés parYstad [12] etStr?m [8, 9, 10, 11]. Le 25 février 1971, de nouveaux échantillons d’eau ont été prélevés dans le fjord pour étudier si, dans les 20 dernières années, d’éventuels changements étaient survenus. Les tableaux présentés contiennent les données chimiques, ainsi que le pH, la température et le taux d’oxygène. En plus, l’eau ?captivée? est comparée avec l’eau de mer originale, au même taux de salinité. Il est difficile de s’exprimer sur les changements survenus dans l’eau, à cause de l’incertitude concernant les mesures de profondeur. Cependant, on n’a pas observé une dite semi-stagnation comme l’a décriteStróm [8] (fig. 3). Il est possible qu’environ un mètre de cette eau ?captivée? se soit perdue, durant les 20 dernières années, par la disparition de la semi-stagnation.

     

Long-term effects of anthropogenic CO<Subscript>2</Subscript> emissions simulated with a complex earth system model

A new complex earth system model consisting of an atmospheric general circulation model, an ocean general circulation model, a three-dimensional ice sheet model, a marine biogeochemistry model, and a dynamic vegetation model was used to study the long-term response to anthropogenic carbon emissions. The prescribed emissions follow estimates of past emissions for the period 1751–2000 and standard IPCC emission scenarios up to the year 2100. After 2100, an exponential decrease of the emissions was assumed. For each of the scenarios, a small ensemble of simulations was carried out. The North Atlantic overturning collapsed in the high emission scenario (A2) simulations. In the low emission scenario (B1), only a temporary weakening of the deep water formation in the North Atlantic is predicted. The moderate emission scenario (A1B) brings the system close to its bifurcation point, with three out of five runs leading to a collapsed North Atlantic overturning circulation. The atmospheric moisture transport predominantly contributes to the collapse of the deep water formation. In the simulations with collapsed deep water formation in the North Atlantic a substantial cooling over parts of the North Atlantic is simulated. Anthropogenic climate change substantially reduces the ability of land and ocean to sequester anthropogenic carbon. The simulated effect of a collapse of the deep water formation in the North Atlantic on the atmospheric CO₂ concentration turned out to be relatively small. The volume of the Greenland ice sheet is reduced, but its contribution to global mean sea level is almost counterbalanced by the growth of the Antarctic ice sheet due to enhanced snowfall. The modifications of the high latitude freshwater input due to the simulated changes in mass balance of the ice sheet are one order of magnitude smaller than the changes due to atmospheric moisture transport. After the year 3000, the global mean surface temperature is predicted to be almost constant due to the compensating effects of decreasing atmospheric CO₂ concentrations due to oceanic uptake and delayed response to increasing atmospheric CO₂ concentrations before.     

Airborne gravimetry used in precise geoid computations by ring integration

Two detailed geoids have been computed in the region of North Jutland. The first computation used marine data in the offshore areas. For the second computation the marine data set was replaced by the sparser airborne gravity data resulting from the AGMASCO campaign of September 1996. The results of comparisons of the geoid heights at on-shore geometric control showed that the geoid heights computed from the airborne gravity data matched in precision those computed using the marine data, supporting the view that airborne techniques have enormous potential for mapping those unsurveyed areas between the land-based data and the off-shore marine or altimetrically derived data. Received: 7 July 1997 / Accepted: 22 April 1998     

A flexible gravity corer based on a plastic funnel closing principle

A highly flexible and efficient gravity corer, easy to construct from inexpensive and readily available material, is described. Barrels of various length can be swiftly interchanged according to requirements in the field. Hollow weights can easily be adjusted to the most appropriate height of the barrel. The simple but reliable closing valve (constructed of two plastic funnels) can be adapted to other types of gravity corers as well. Several useful modifications of the corer are discussed.     

Palaeomagnetic evidence for large-scale dextral movement along the Trollfjord-Komagelv Fault,Finnmark, north Norway

Palaeomagnetic data from Late Precambrian dykes from the northern part of Varanger peninsula, north Norway, suggest a two-axis magnetization structure. The dominant component is considered to be syn- to late-tectonic and probably acquired at around 640 m.y. B.P. Superposed on this magnetization is a minor component which is compatible with the relative Lower-Middle Palaeozoic field; i.e. it was most likely imposed during the climax of the Caledonian orogenic movements in north Norway. The estimated relative Late Precambrian palaeopole cannot easily be reconciled with the European Late Precambrian polar path. This disagreement can be accounted for by assuming a post-magnetization dextral megashear, of the order of 500–1000 km, along the Trollfjord-Komagelv fracture zone. This type of displacement is in line with geological evidence and the palaeomagnetic reconstruction supports the long-held view of there having been continuity between the depositional environments of the Varanger Peninsula Barents Sea Group, the Eleonore Bay Group of east Greenland and the Hecla Hoek Formation of east Spitsbergen. The character and age of the horizontal displacement, post-640 to pre-500 m.y. B.P., is seen in conjunction with the opening up of the lapetus Ocean and reactivation of ancient deep-seated fractures during both the spreading and the contraction phases of ocean development.     

Mineral zoning as a record of P,T history of Precambrian eclogites and schists in western Tasmania

Ferromagnesian minerals, particularly garnet but also phengite, omphacite and talc, from eclogites and surrounding schists from the Lyell Highway-Collingwood river area, western Tasmania are compositionally zoned.In rocks which have suffered little secondary alteration the Mg-value ($\text{100 Mg}\text{Mg+Fe}{}^{\mathrm{++}}$) of granets increases from core to rim, while the Mg-value of the most important coexisting ferromagnesian phases (clinopyroxene, phengite and talc in different assemblages) decreases from core to rim. CaO decreases from core to rim in garnet. MnO may show little or no variation in garnet, or decrease from core to rim.When compared with experimental data, the zoning of these minerals can be uniquely explained by growth during changing P,T conditions. The eclogites and the surrounding schists have the same prograde P,T history.When determining the K_D-values of garnet and its coexisting ferromagnesian phases it is important to consider secondary rim alterations as well as the prograde zoning of the mineral.     

A convenient,one-hand-operated field burette

A simple, cheap and easily constructable burette, particularly useful for alkalinity, dissolved oxygen and hardness titration is described. Precise titrant delivery (<1 μl) is controlled by a handy ‘clothespin valve’ connected to the lower opening of appropriately sized graduated pipettes or burette tubes. The burette is small, flexible and easily portable and should be highly recommended as an all round field burette for limnochemists.     

Temperature and pressure dependence of Fe-Mg partitioning between garnet and phengite,with particular reference to eclogites

Experimental data combined with data from natural rocks have been used to calibrate a geothermometer based on the distribution of Fe²⁺ and Mg between coexisting garnets and phengites. The pressure effect on the K _D -value appears to be considerable. The calculated thermometer is expressed as $$T(K) = \frac{{3685 + 77.1P(kb)}}{{InK_D + 3.52}}.$$ The use of this \(K_{D_{(FeO/MgO)} }^{ga + ph}\) geothermometer on eclogites with low Fe₂O₃ content, gives P-T values which are in good accordance with those obtained by other methods. The problems that arise when Fe³⁺ is present in larger amounts, are discussed.     

Schiller effects and exsolution in sodium-rich plagioclases

Plagioclase feldspars with mean compositions Ab_91,3Or_4,7An_4,0 and Ab_88,7An_10,1Or_1,2 have been studied by transmission electron microscopy and electron diffraction. The substructure consists of thin lamellae of albite and oligoclase. Two types of orientations of the lamellar planes were observed. The orientation of the more common type was found to change from (08 \(\bar 1\) ) to about ( \(\bar 1\) , 21, \(\bar 2\) ) as a function of the mean potassium content. The plane of the other type was found to be near ( \(\bar 7\) 12). Only the first type of lamellae produces visible Schiller colours.     

Talc-garnet-kyanite-quartz schist from an eclogite-bearing terrane,Western Tasmania

Talc-garnet-kyanite-quartz schist occurs in an eclogite-bearing terrane in the Precambrian of Western Tasmania. It is argued that this rock was formed at a pressure of ? 10 kb and a temperature of 600°±20° C. Chemical zoning in the garnet and talc preserves evidence of increasing temperature during growth of the major minerals.