Vertical flux of biogenic matter during a Lagrangian study off the NW Spanish continental margin

Lagrangian experiments with short-term, drifting sediment traps were conducted during a cruise on RRS Charles Darwin to the NW coast of Spain to study the vertical flux and composition of settling biogenic matter. The cruise was split into two legs corresponding to (i) a period of increased production following an upwelling event on the continental shelf (3–10 August 1998) and (ii) an evolution of a cold water filament originating from the upwelled water off the shelf (14–19 August). The export of particulate organic carbon (POC) from the upper layer (0–60m) on the shelf was 90–240mgC.m⁻².d⁻¹ and off the shelf was 60–180mgC.m⁻².d⁻¹. Off shelf the POC flux at 200m was 50–60mg.m⁻².d⁻¹. A modest sedimentation of diatoms (15–30mgC.m⁻².d⁻¹) after the upwelling was associated with increased vertical flux of chlorophyll a (1.8–2.1mg.m⁻².d⁻¹) and a decrease of the POC:PON molar ratio of the settled material from 9 to 6.4. Most of the pico-, nano-, and microplankton in the settled material were flagellates; diatoms were significant during the on shelf and dinoflagellates during the off shelf leg. Off shelf, the exponential attenuation of POC flux indicated a strong retention capacity of the plankton community between 40 and 75m. POC:PON ratio of the settled particulate matter decreased with depth and the relative portion of flagellates increased, suggesting a novel, flagellate and aggregate mediated particulate flux in these waters. Export of POC from the euphotic layer comprised 14–26% of the integrated primary production per day during the on shelf leg and 25–42% during the off shelf leg, which characterises the importance of sedimentation in the organic carbon budget of these waters.     

The fate of production in the central Arctic Ocean - top-down regulation by zooplankton expatriates?

We estimated primary and bacterial production, mineral nutrients, suspended chlorophyll a (Chl), particulate organic carbon (POC) and nitrogen (PON), abundance of planktonic organisms, mesozooplankton fecal pellet production, and the vertical flux of organic particles of the central Arctic Ocean (Amundsen basin, 89-88° N) during a 3 week quasi-Lagrangian ice drift experiment at the peak of the productive season (August 2001). A visual estimate of ≈15% ice-free surface, plus numerous melt ponds on ice sheets, supported a planktonic particulate primary production of 50-150 mg C m⁻² d⁻¹ (mean 93 mg C m⁻² d⁻¹, n = 7), mostly confined to the upper 10 m of the nutrient replete water column. The surface mixed layer was separated from the rest of the water column by a strong halocline at 20 m depth. Phototrophic biomass was low, generally 0.03-0.3 mg Chl m⁻³ in the upper 20 m and <0.02 mg Chl m⁻³ below, dominated by various flagellates, dinoflagellates and diatoms. Bacterial abundance (typically 3.7-5.3 × 10⁵, mean 4.1 × 10⁵ cells ml⁻¹ in the upper 20 m and 1.3-3.7 × 10⁵, mean 1.9 × 10⁵ cells ml⁻¹ below) and Chl concentrations were closely correlated (r = 0.75). Mineral nutrients (3 μmol NO₃ l⁻¹, 0.45 μmol PO₄ l⁻¹, 4-5 μmol SiO₄ l⁻¹) were probably not limiting the primary production in the upper layer. Suspended POC concentration was ∼30-105 (mean 53) mg C m⁻³ and PON ∼5.4-14.9 (mean 8.2) mg N m⁻³ with no clear vertical trend. The vertical flux of POC in the upper 30-100 m water column was ∼37-92 (mean 55) mg C m⁻² d⁻¹ without clear decrease with depth, and was quite similar at the six investigated stations. The mesozooplankton biomass (≈2 g DW m⁻², mostly in the upper 50 m water column) was dominated by adult females of the large calanoid copepods Calanus hyperboreus and Calanus glacialis (≈1.6 g DW m⁻²). The grazing of these copepods (estimated via fecal pellet production rates) was ≈15 mg C m⁻² d⁻¹, being on the order of 3% and 20% of the expected food-saturated ingestion rates of C. hyperboreus and C. glacialis, respectively. The stage structure of these copepods, dominated by adult females, and their unsatisfied grazing capacity during peak productive period suggest allochthonous origin of these species from productive shelf areas, supported by their long life span and the prevailing surface currents in the Arctic Ocean. We propose that the grazing capacity of the expatriated mesozooplankton population would match the potential seasonal increase of primary production in the future decreased ice perspective, diminishing the likelihood of algal blooms.     

Einige Vereinfachungen der Chlor-Titration für biologische und wasserbaukundliche Zwecke in Küstengewässern

Zusammenfassung Für viele Zwecke der Salzgehaltsbestimmung von Meerwasserproben in Küstenn?he ist die Einhaltung der üblichen Fehlergrenze von 0,01%Cl, wie sie für wissenschaftlich-ozeanographische Untersuchungen auf offener See vorgeschrieben ist, nur selten erforderlich. Lockert man dementsprechend diese extreme Genauigkeitsanforderung in geringem Ma?e, so lassen sich einige methodische Vereinfachungen in den Arbeitsgang einführen, die einmal die Benutzung der Knudsen-Tabelle und des Kopenhagener Normalwassers überflüssig machen und zum anderen durch Umwandlung in eine Mikromethode (0,75 ccm Meerwasser pro Untersuchungsprobe) zu einem erheblichen Zeitgewinn führen.

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Some simplifications of the chlorinetitration of samples from coastal waters for use by biologists and hydraulic engineers

Summary When determining the salinity of sea water samples from coastal areas it is often superfluous to observe the accuracy of 0,01‰Cl required for scientific oceanographic investigations in the open sea. If, therefore, this demand for extreme accuracy is relaxed a trifle it becomes possible to introduce some methodical simplifications which on the one hand make it unnecessary to use the Knudsen tables and the Copenhagen standard water and on the other hand are very economical in time and size of sample (0,75 ccm sea water in each sample)

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Quelques simplifications relatives au titrage de chlore à l'usage de biologistes et d'ingénieurs hydrauliciens

Résumé En déterminant la salinité des prises d'eau cueillies près de la c?te il n'est guère nécessaire d'observer la précision de 0,01%Cl comme cela est exigé en cas des investigations océanographiques de la haute mer. Si l'on diminue cette exigence de précision extrême il est possible d'introduire quelques simplifications méthodiques qui d'une part feront inutile l'usage des tableaux de Knudsen et de l'eau normale de Copenhague et d'autre part permettront de limiter la quantité d'eau de mer à 0,75 ccm par échantillon ce qui économisera beaucoup de temps.

     

Zur Frage der inneren thermischen Unruhe des Meeres

Ohne Zusammenfassung     

Ein einfaches Klein-Aräometer zur exakten Bestimmung des Salzgehaltes im Meerwasser

Zusammenfassung Im folgenden wird eine neuartige Aräometer-Apparatur zur Dichte- und Salzgehaltsbestimmung von Meerwasserproben beschrieben. Vor ähnlichen Apparaten zeichnet sie sich durch folgende Punkte aus:Sie ist besonders klein und kompakt gebaut und benötigt mit Vorspülen nur 60 bis 80 ccm Meerwasser. — Der Aräometer-Schwimmer selbst hat ein Volumen von nur 7 ccm. Dadurch, daß er an einem Härchen aufgehängt und die Oberflächenspannung durch Zugabe einiger Tropfen einer Detergenz-Lösung aufgehoben ist, wird ein reibungsloses Gleiten des Schwimmers ermöglicht. — Infolgedessen läßt sich der Auftrieb mit der großen Genauigkeit von 0,05 mg messen, was einer Empfindlichkeit von 0,01 S entspricht. — Als Meßinstrument dient eine kompakt gebaute Tor-sionswaage mit kreisförmiger Ableseskala, die sich in bequemer Höhe zum Auge befindet. Der Gesamtwägebereich umfaßt 200 mg, so daß der gesamte ozeanische Meßbereich von 0 bis 40 S ohne Schwimmerwechsel erfaßbar ist. — Gegenüber der Titration des Cl-Gehaltes hat die Methode den Vorteil, daß bei etwas erhöhter Empfindlichkeit und Arbeitsgeschwindigkeit im Serienbetrieb die Ablesung des Zeigers und des Thermometers wesentlich weniger ermüdend ist als die diffizile tropfenweise Zugabe der Silbernitratlösung und die Beobachtung des Indikatorumschlagpunktes. — Die Endberechnung des Salzgehaltes erfolgt über die beiden beobachteten Werte von Gewicht (an der Torsionswaage) und Temperatur (am Thermometer) und mit Hilfe einer bequem ablesbaren Fluchtentafel. — Der Meßvorgang selbst erfordert weder Chemikalien noch den Anschluß von Wasser oder elektrischem Strom.

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A simple small-type areometer for the precise determination of salinity and density in seawater

Summary The present paper describes a newly developed areometer for the determination of salinity and density of sea-water. The apparatus is distinguished by the following features:The areometer is extremely small, its construction is very compact; including preliminary rinsing, it requires only 60 to 80 cm³ of sea-water. The volume of the areometer float itself is 7 cm³ only. Besides, by suspending the float by a fine hair and suppressing surface tension by adding a few drops of detergent solution the float is enabled to slide without friction. Owing to these two operations, the weight can be determined with so high an accuracy as 0,05 mg, corresponding to a sensitivity of 0,01 S. — A compact torsion-balance which, at a convenient height, includes a circular reading scale, serves as a measuring instrument. The total weighing range of the balance amounts to 200 mg, thus enabling the entire oceanic measuring range from 0 to 40 S to be determined without having to change the float. — In comparison with chlorinity titration the new method offers the advantage of an increased sensitivity and a higher working speed, since in serial investigations reading of the indicator needle and of the thermometer is far less tiring than the troublesome addition of silver nitrate solution and the simultaneous observation of the equivalance point. — The definitive determination of salinity is carried out with the aid of the two observed values of weight (on the torsion balance) and temperature (on the thermometer) and a conveniently readable nomograph. — The measuring procedure requires neither the use of chemicals, nor water connection, nor power equipment.Résumé Le travail actuel décrit un nouvel aréomètre pour déterminer la salinité et la densité des échantillons d'eau de mer. Cet appareil est caractérisé par sa petitesse, par sa construction compacte, par la quantité insignifiante d'eau de mer de 60 à 80 cm³ qu'il demande, y compris l'eau pour le rincement préalable, et par le petit volume de seulement 7 cm³ de son flotteur. De plus, en suspendant le flotteur par un cheveu fin et en supprimant la tension superficielle de liquide par l'addition de plusieurs gouttes d'une solution de détersion on réussit à faire glisser sans friction le flotteur. Ces deux opérations permettent de mesurer le poids à l'extrême précision de 0,05 mg près, ce qui est identique à la sensibilité de 0,01 S. — Pour des mesures on se sert d'une balance compacte à torsion munie d'une échelle circulaire à lecture. Cette échelle se trouve installée à une hauteur convenable aux yeux. L'étendue totale de la balance va jusqu'à 200 mg, ce qui permet d'étudier l'entière étendue de mesure océanique de 0 à 40 S sans changer de flotteur. — Confrontant la méthode de titrage du chlore avec la nouvelle méthode, on remarquera que la lecture de l'aiguille et du thermomètre est beaucoup moins fatigante que la pénible addition par gouttes du nitrate d'argent et l'observation simultanée du moment de l'équilibre, surtout dans le cas où les circonstances demandent l'observation d'une sensibilité un peu élevée ou une plus grande rapidité de travail lors des recherches en série. — Le calcul définitif de la salinité se fait à l'aide de deux valeurs observées, à savoir le poids (sur la balance à torsion) et la température (sur le thermomètre), et au moyen d'un nomogramme bien lisible. — La méthode de mesure elle-même ne demande ni emploi de substances chimiques, ni distribution d'eau, ni installation d'énergie.

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Un aréomètre de simple construction pour la précise détermination de la salinité et de la densité de l'eau de mer

     

Geophysical research on the Kärdla impact structure,Hiiumaa Island,Estonia

Abstract— The 4 km wide and 500 m deep circular Kärdla impact structure in Hiiumaa Island, Estonia, of middle Ordovician age (～455 Ma), is buried under Upper Ordovician and Quaternary sediments. To constrain the geophysical models of the structure, petrophysical properties such as magnetic susceptibility, natural remanent magnetization (NRM), density, electrical conductivity, porosity and P-wave velocity were measured on samples of crystalline and sedimentary rocks collected from drill cores in different parts of the structure and the surrounding area. The results were used to interpret the central gravity anomaly of ?3 mGal and the magnetic anomaly of ?100 nT and also the surrounding weak positive anomalies revealed by high precision survey data. The unshocked granitic rocks outside the structure have a mean density of ～2630 kgm^?3. Their shocked counterparts have densities of ～2400 kgm^?3 at a depth of ～500 m, increasing up to 2550 kgm^?3 at a depth of 850 m. Porosity and electrical conductivity decrease, but P-wave velocity increases as density increases away from the impact point. Thus, the gradual changes in the physical properties of the rocks as a function of radial distance from the crater centre are consistent with an impact origin for Kärdla. As in many other impact structures, the magnetization of the shocked rocks are also clearly lower than those of unshocked target rocks. A new geophysical and geological model of the Kärdla structure is presented based on geophysical field measurements and data on gradual changes in petrophysical parameters of the shocked target and overlying rocks, together with structural data from numerous boreholes. An important feature of this model is the lack of an observable geophysical signature of the central uplift observed in drillcores.     

Specific affinity for phosphate uptake and specific alkaline phosphatase activity as diagnostic tools for detecting phosphorus-limited phytoplankton and bacteria

We analyzed responses of soluble reactive phosphorus (SRP), bioavailable phosphate (PO₄), particulate phosphorus, turnover time of orthophosphate (T_t), and alkaline phosphatase activity (APA) to varying degrees of nutrient stress. The nutrient stress was evoked by different treatments in concentration and combination of inorganic nitrogen (N) and phosphorus (P), and labile organic carbon (glucose) to mesocosms in experiments carried out in eutrophic southern (Odense Fjord, Denmark) and northern (Tvärminne Archipelago, Finland) coastal zones of the Baltic Sea. Despite seasonal and geographical differences, similar responses were observed in both experiments. Low SRP (<100 nmol l^?1), shortT _t (<10 h), and increased levels of APA were observed in both N+P balanced and P deficient treatments, while the opposite trend was observed in P replete treatments. The shortestT _t and the highest APA were found when glucose was combined with N treatment. Bioavailable PO₄ was estimated usingT _t and P uptake rates as derived from stoichiometric conversion of carbon based primary and bacterial production. With shorterT _t, the PO₄ pool declined to <1 nmol-P l^?1, whereas the SRP background pool (difference between SRP and PO₄) remained relatively constant (c. 50 nmol l^?1). APA was inversely related to PO₄ but not to SRP. Responses of specific APA and specific affinity for PO₄ uptake, which are APA and PO₄ uptake rates (inverse ofT _t), respectively, normalized to the summed P biomass of phytoplankton and bacteria, responded consistently to the pattern and magnitude of nutrient limitation evoked in our experiments. Our results, together with a literature survey, suggest that both parameters can be useful in examining PO₄ availability for the natural phytoplankton and bacteria community in P starved aquatic systems.