The behaviour of dissolved Cd, Co, Zn, and Pb in North Atlantic near-surface waters (30°N/60°W–60°N/2°W)

In September 1993 (M26) and June/July 1996 (M36), a total of 239 surface samples (7 m depth) were collected on two transects across the open Atlantic Ocean (224 samples) and northwest European shelf edge area. We present an overview of the horizontal variability of dissolved Cd, Co, Zn, and Pb in between the northwest and northeast Atlantic Ocean in relation to salinity and the nutrients. Our data show a preferential incorporation of Cd relative to P in the particulate material of the surface ocean when related to previously published parallel measurements on suspended particulate matter from the same cruise. There is a good agreement with results recently estimated from a model by Elderfield and Rickaby (Nature 405 (2000) 305), who predict for the North Atlantic Ocean a best fit for α_Cd/P=[Cd/P]_POM/[Cd/P]_SW of 2.5, whereas the approach of our transect shows a α_Cd/P value of 2.6. The Co concentrations of our transects varied from <5 to 131 pmol kg⁻¹, with the lowest values in the subtropical gyre. There were pronounced elevations in the low-salinity ranges of the northwest Atlantic and towards the European shelf. The Co data are decoupled from the Mn distribution and support the hypothesis of marginal inputs as the dominant source. Zinc varied from a minimum of <0.07 nmol kg⁻¹ to a maximum of 1.2 and 4.8 nmol kg⁻¹ in regions influenced by Labrador shelf or European coastal waters, respectively. In subtropical and northeast Atlantic waters, the average Zn concentration was 0.16 nmol kg⁻¹. Zinc concentrations at nearly three quarters of the stations between 40°N and 60°N were <0.1 nmol kg⁻¹. This suggests that biological factors control Zn concentrations in large areas of the North Atlantic surface waters. The Pb data indicated that significant differences in concentration between the northwest and northeast Atlantic surface waters presently (1996) do not exist for this metal. The transects in 1993 and 1996 exhibited Pb concentrations in the northeast Atlantic surface waters of 30 to 40 pmol kg⁻¹, about a fifth to a quarter of the concentrations observed in 1981. This decline is supported by our particle flux measurements in deep waters of the same region.     

An Unusual Bluegreen Alga Symbiotic with Two New Species of Ulosa (Porifera: Hymeniacidonidae) from Carrie Bow Cay,Belize*

Abstract. Two new species of the sponge genus Ulosa were found living in symbiosis with a chroococcacean cyanophyte (cyanobacterium) in shallow Caribbean coral reefs off Belize (Central America). Ulosa funicularis is a stringy green sponge (styles: 157 × 2.5 μm, mean dimensions); U. arenosa is a thickly encrusting, shaggy, brownish-greenish mottled species with sandy ectosome (styles: 175 × 3.6 μm). The endosymbiotic algae make up 50% of the cellular sponge tissue. The algal cells are light green, spherical, 5–9 μm in diameter, and divide by median constriction. Electron microscopy shows that cell walls are fully developed but that thylakoids are unusual for their inflated sacs, which are in communication with the nucleoplasmic regions. Although the pigment composition is typical for the Cyanophyta, the phycobiliproteins occur in considerably     

A New Plankton Sampler for Coral Reefs

Abstract. A new self-contained Horizontal Plankton Sampler (HOPLASA) collects near-reef plankton that is not captured by conventional net tows and emergence traps. An electrical motor-propeller assembly inside a large acrylic cylinder drives water past an in-line flowmeter and through a rigidly attached plankton net. When positioned in the coral reef environment this sampling gear filters known quantities of bottom water. Larvae and developmental stages of many invertebrates and some fishes that never migrate to upper water layers but constitute an important fraction of the food chain are captured. Larvae of sponges, corals, and gorgonians, the most important animal reef builders, are obtained live and undamaged and can be cultured in the laboratory for identification after metamorphosis.     

Der Einfluß des Windes auf die Wasserbewegungen durch die Straße von Dover

Zusammenfassung Es werden die Beziehungen zwischen den über der südlichen Nordsee herrschenden Winden und den durch die Straße von Dover stattfindenden Wasserbewegungen abgeleitet. Diese werden einerseits durch den unmittelbaren Windeinfluß und andererseits durch das im wesentlichen auch windbedingte Gefälle vom Kanal zur Nordsee bestimmt. Der Jahresgang und im Zusammenhang damit das Vorrücken salzreichen Wassers im Kanal werden untersucht. Die bei Feuerschiff Varne auftretenden Richtungsänderungen des mittleren jährlichen Reststromes werden durch Schwankungen der Windgeschwindigkeit erklärt. An Hand von Salzgehaltskarten aufeinanderfolgender Monate werden Bewegungen von Wasserkörpern und Fronten im Kanal unter dem Einfluß des Windes verfolgt. Auf die Bedeutung solcher Untersuchungen synoptischer Art zum Studium der Wasserbewegungen wird hingewiesen.

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The wind's influence on the flow of water through the Straits of Dover

Summary The relations between the winds blowing over the southern North Sea and the flow of water through the Straits of Dover are derived; this flow of water depends on both the immediate influence of the wind and the slope of the sea surface between the Channel and the North Sea which, too, is mainly produced by the wind. The annual variation and, in connection with it, the advance of Atlantic water into the Channel are investigated. The changes of directions the mean annual residual current is subjected to according to the observations made near the light vessel Varne are found to be due to variations in the wind velocity. The shifting of water bodies and fronts in the Channel as dependent on the wind is studied by means of salinity charts over consecutive months. Finally, attention is drawn to the significance of such synoptical investigations for the study of water movements.

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L'influence du vent sur les mouvements de l'eau dans le Pas de Calais

Résumé Les relations entre les vents dominant au sud de la mer du Nord et les mouvements de l'aeu dans le Pas de Calais sont dérivées. Ces mouvements sont causés par l'action immédiate du vent ainsi que par la pente de la surface entre la Manche et la mer du Nord; celle-ci, de sa part, est de même essentiellement causée par le vent. La marche annuelle et, en conséquence, la progression de l'eau atlantique dans la Manche sont étudiées. Les changements de direction du courant résiduel moyen par an dérivés des observations du bateau feu Varne sont expliqués en fonction des changements de vitesse du vent. À l'aide des cartes de salinité sur des mois consécutifs les mouvements des masses d'eau et des fronts dans la Manche sont étudiés par rapport à leur dépendance du vent. En résumé, l'attention est attirée sur l'importance de telles investigations synoptiques pourl'étude des mouvements de l'eau.

     

UNUSUAL WEATHERING PRODUCTS OF OLDHAMITE PARENTAGE IN THE NORTON COUNTY ENSTATITE ACHONDRITE

White, pale-yellow and brown deposits occur on surfaces of fragments of the Norton County enstatite achondrite. X-ray powder analysis of these materials indicates that they consist of several calcium-bearing minerals: portlandite [Ca(OH)₂], vaterite (CaCO₃, hexagonal), calcite (CaCO₃, trigonal) and bassanite (CaSO₄-1/2 H₂O). We suggest that these minerals formed by weathering of oldhamite (CaS), which we found to occur in Norton County. The occurrence of portlandite suggests that at low temperatures and in the terrestrial environment, hydrolysis of oldhamite is the most important first step in the weathering sequence. Subsequent carbonation of portlandite is thought to produce vaterite, and vaterite in turn might transform into calcite. Thus, we suggest a weathering sequence in the terrestrial environment of oldhamite portlandite vaterite calcite. The mineral bassanite is clearly also a terrestrial weathering product but its precise mode of origïn is somewhat uncertain: in the system CaSO₄-H₂O, bassanite forms from gypsum at about 100 °C (an unlikely high T for the weathering environment of Norton County).     

The Chassigny meteorite: a cumulate dunite with hydrous amphibole-bearing melt inclusions

The Chassigny meteorite is a moderately shocked olivine achondrite or chassignite with features indicative of a cumulate origin with some subsolidus annealing. Chassigny is an iron-rich dunite (Fo₆₈) with minor amounts of Ca-rich and Ca-poor pyroxene, alkalic feldspar, chromite, and melt inclusions in olivine. Accessory phases include chlorapatite, troilite, marcasite, kaersutite amphibole, pentlandite, ilmenite, rutile and baddeleyite. The meteorite experienced shock pressures of ~150–200 kbar as evidenced by planar and irregular fractures in olivine, local recrystallization in pyroxene and reduced birefringence and rare deformation lamallae in feldspar. Kaersutitic amphibole (K_0.05 Na_0.45)_0.50 (Ca_1.71 Na_0.29)_2.00 (Mg_2.73 ‘Fe’_1.19 Ti_0.73 A1_0.23 Cr_0.08 Mn_0.03)_4.99 (Si_6.05Al_1.95)_8.00 O₂₂ (OH, F)₂ containing hydrogen and lesser amounts of fluorine represents the first extraterrestrial occurrence of hydrous amphibole and the first meteoritic amphibole type other than fluorichterite. Kaersutite is found only in melt inclusions.Melt inclusion bulk compositional data suggest crystallization from a low-Ca melt that may have been similar in major element abundances to the silicate portion of LL group chondrites. However, Chassigny has a fractionated pattern for REE and the lack of metallic iron, possible presence of minor Ni in the olivine and Fe³⁺ in the chromites indicates that Chassigny formed under relatively more oxidizing conditions than most other achondrites. Therefore its parental melt could not have been directly derived from a chondritic composition in a simple single-stage process. The iron-rich bulk composition, cumulate texture and abundance as well as alkalic nature of the interstitial feldspar indicate that Chassigny could not have generated eucritic magmas. This places further constraints on its relationship to other meteorites and the parent body from which it is derived. The Brachina meteorite is similar to Chassigny except that it is finer grained, more feldspathic and is unshocked. It extends the fractionation range of this group which now represents two unusual meteorites.     

Recent changes of the thermohaline circulation in the subpolar North Atlantic

Time series of hydrographic sections in the northern North Atlantic from the period 1990 to 2004 are analyzed for changes in the characteristics and distribution of water masses that are involved in the thermohaline circulation (THC). During the 1990s, the North Atlantic Oscillation (NAO) alternates from a positive phase (strong westerlies) to a negative phase (weak westerlies). The reduced ocean heat loss confined the convection in the Labrador Sea to the upper 1,200 m, generating a new salinity minimum layer characterizing the Upper Labrador Sea Water (ULSW), and led to a warming and salinization of the older LSW below due to lateral mixing. The Lower LSW, formed in the first half of the 1990s, spread in the subpolar gyre and reached the Newfoundland and Irminger basins after about 1 to 2 years, where the associated isopycnal doming contributed to eastward frontal shifts in the upper layer. After 5 and 6 years, it arrived in the Iceland and West European basins, respectively. The collapse of the isopycnal dome in the Labrador Sea, associated with the drainage of the Lower LSW, resulted in a slowing of the cyclonic circulation of the subpolar gyre. This was accompanied in the upper layer by a westward shift of the southeastern extension of the gyre and a northward advection of warm and saline subtropical water in its eastern part, which finally reached the Labrador Sea after about 7 years. In the upper layer of the Labrador Sea, the advection of warm and saline water dominated over the heat loss to the atmosphere and the freshwater gain from melting ice and precipitation in the NAO-low period, so that no accumulation of freshwater but an increase of the heat and salt contents were observed, as in the whole eastern part of the subpolar gyre. Within 1 to 2 years after the drop of the NAO in the winter of 1995/1996, the Subarctic (Subpolar) Front shifted northward and westward north of about 50°N, favored by the retreat of the low-salinity tongue extending eastward from the southern Labrador Sea, and it shifted southward and eastward in the Newfoundland Basin. Therefore, the enhanced northward advection of subtropical waters in the northeastern North Atlantic is balanced by the enhanced southward advection of subarctic waters, including Lower LSW in the Newfoundland Basin, indicating a strong response of the gyre component of the THC.