Oceanic bubble population measurements using a buoy-deployedcombination frequency technique

This paper presents the results of using a combination frequency acoustic technique to measure the near-surface bubble population in the open sea. The combination frequency technique monitors the appearance of sum-and-difference signals generated by the nonlinear interaction of two sound fields: one, a high-frequency signal, scatters geometrically from the bubble, and the other, of much lower frequency, is used to excite the bubble into resonant pulsation. The text details the calibration of the apparatus necessary to relate the measured heights of the sum-and-difference terms to actual numbers of bubbles and describes the experimental procedure for the collection of the oceanic data. In total, six trials were performed over a one-day period, each comprising ten “snapshots” of the local bubble population at ten discrete radii. This data was augmented with simultaneous video, slide, and dictaphone records of the state of the sea around the measurement position     

Optical moorings-of-opportunity for validation of ocean color satellites

Buoy-mooring platforms are advantageous for time-series validation and vicarious calibration of ocean color satellites because of their high temporal resolution and ability to perform under adverse weather conditions. Bio-optical data collected on the Bermuda Testbed Mooring (BTM) were used for comparison with satellite ocean color data in an effort to further standardize sampling and data processing methods for high quality satellite-mooring comparisons. Average percentage differences between satellite-measured and mooring-derived water leaving radiances were about 20% at the blue wavelengths, decreasing to as low as 11% in the blue-green to green wavebands. Based on a series of data processing methods and analyses, recommendations concerning rigor of quality control for collected data, optimal averaging of high-frequency data, sensor self-shading wind corrections, and instrumentation placement requirements are given for the design and application of optical moorings for ocean color satellite validation. Although buoy-mooring platforms are considered to be among the very best methods to validate ocean color satellite measurements, match-up discrepancies due to water column variability and atmospheric corrections remain important issues.     

Physical dynamics and biological implications of a mesoscale eddy in the lee of Hawai’i: Cyclone Opal observations during E-Flux III

E-Flux III (March 10–28, 2005) was the third and last field experiment of the E-Flux project. The main goal of the project was to investigate the physical, biological and chemical characteristics of mesoscale eddies that form in the lee of Maui and the Island of Hawai’i, focusing on the physical–biogeochemical interactions. The primary focus of E-Flux III was the cyclonic cold-core eddy Opal, which first appeared in the NOAA GOES sea-surface temperature (SST) imagery during the second half of February 2005. During the experiment, Cyclone Opal moved over 160 km, generally southward. Thus, the sampling design had to be constantly adjusted in order to obtain quasi-synoptic observations of the eddy. Analyses of ship transect-depth profiles of CTD, optical and acoustic Doppler current profiler (ADCP) data revealed a well-developed feature characterized by a fairly symmetric circular shape with a radius of about 80 km. Depth profiles of temperature, salinity and density were characterized by an intense doming of isothermal, isohaline and isopycnal surfaces. Isopleths of nutrient concentrations were roughly parallel to isopycnals, indicating the upwelling of deep nutrient-rich water. The deep chlorophyll maximum layer (DCML) shoaled from a depth of about 130 m in the outer regions of the eddy to about 60 m in the center. Chlorophyll concentrations reached their maximum values in Opal's core region (about 40 km in diameter), where nutrients were upwelled into the euphotic layer. ADCP velocity data clearly showed the cyclonic circulation associated with Opal. Vertical sections of tangential velocities were characterized by values that increased linearly with radial distance from near zero close to the center to a maximum of about at roughly 25 km from the center, and then slowly decayed. The vertical extent of the cyclonic circulation was primarily limited to the upper mixed layer, as tangential velocities decayed quite rapidly within a depth range of 90–130 m. Potential vorticity analysis suggests that only a relatively small (about 50 km in diameter) and shallow (to a depth of approximately 70 m) portion of the eddy is isolated from the surrounding waters. Radial movements of water can occur between the center of the eddy and the outer regions along density surfaces within an isopycnal range of σ–t_23.6 () and σ–t_24.4 (). Thus the biogeochemistry of the system might have been greatly influenced by these lateral exchanges of water at depth, especially during Opal's southward migration. While the eddy was translating, deep water in front of the eddy might have been upwelled into the core region, leading to an additional injection of nutrients into the euphotic zone. At the same time, part of the chlorophyll-rich waters in the core region might have remained behind the translating eddy and, thus contributed to the formation of an eddy wake characterized by relatively high chlorophyll concentrations.     

Application of underwater optical data to estimation of primary productivity

We conducted time-series observations of optical fields near the base of the euphotic zone (approximately 40 m) using moored automatic optical sensors at a time-series station in the Western Pacific Subarctic Gyre from March 2005 to July 2006 (with some gaps). We used the ratio of photosynthetically available radiation at the surface (surface PAR) to in situ quantum irradiance (in situ QI) at about 40 m as an index of opacity (surface PAR/in situ QI), which began to increase in the middle of April and peaked between the end of June and the middle of July 2005. This ratio then decreased toward winter. The ratio increased again beginning in January 2006, and large peaks were observed in June and July 2006. As an index of chlorophyll abundance we used the ratio of spectral irradiance at wavelengths of 555 and 443 nm (Ed₅₅₅/Ed₄₄₃) at about 40 m; seasonal variability of this ratio synchronized well with the attenuation coefficient “k” estimated with surface PAR, in situ QI, and BLOOMS depth. We estimated primary productivity (PP) using Ed₅₅₅/Ed₄₄₃ and an empirical equation based on a previous model but improved on the basis of shipboard observations. Estimated PP agreed well with observed PP. Seasonal variability of estimated PP was synchronized with that of organic carbon flux observed by sediment traps from approximately 150, 540, 1000, and 5000 m. This study demonstrates that time-series observations of in situ optical fields could contribute to the estimation of primary productivity and the study of the biological pump in the ocean.     

Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: Laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA)

Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O₂ and Mn²⁺ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O₂ is not a direct oxidant for Mn²⁺. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe²⁺, H₂S and soluble molecular FeS clusters (FeS_aq) are detected indicating that the reactants for the pyrite formation reaction are H₂S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O₂ and H₂S anti-correlate and that H₂S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O₂ and H₂S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit.     

Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH

Ocean acidification due to anthropogenic CO₂ emissions is a dominant driver of long-term changes in pH in the open ocean, raising concern for the future of calcifying organisms, many of which are present in coastal habitats. However, changes in pH in coastal ecosystems result from a multitude of drivers, including impacts from watershed processes, nutrient inputs, and changes in ecosystem structure and metabolism. Interaction between ocean acidification due to anthropogenic CO₂ emissions and the dynamic regional to local drivers of coastal ecosystems have resulted in complex regulation of pH in coastal waters. Changes in the watershed can, for example, lead to changes in alkalinity and CO₂ fluxes that, together with metabolic processes and oceanic dynamics, yield high-magnitude decadal changes of up to 0.5 units in coastal pH. Metabolism results in strong diel to seasonal fluctuations in pH, with characteristic ranges of 0.3 pH units, with metabolically intense habitats exceeding this range on a daily basis. The intense variability and multiple, complex controls on pH implies that the concept of ocean acidification due to anthropogenic CO₂ emissions cannot be transposed to coastal ecosystems directly. Furthermore, in coastal ecosystems, the detection of trends towards acidification is not trivial and the attribution of these changes to anthropogenic CO₂ emissions is even more problematic. Coastal ecosystems may show acidification or basification, depending on the balance between the invasion of coastal waters by anthropogenic CO₂, watershed export of alkalinity, organic matter and CO₂, and changes in the balance between primary production, respiration and calcification rates in response to changes in nutrient inputs and losses of ecosystem components. Hence, we contend that ocean acidification from anthropogenic CO₂ is largely an open-ocean syndrome and that a concept of anthropogenic impacts on marine pH, which is applicable across the entire ocean, from coastal to open-ocean environments, provides a superior framework to consider the multiple components of the anthropogenic perturbation of marine pH trajectories. The concept of anthropogenic impacts on seawater pH acknowledges that a regional focus is necessary to predict future trajectories in the pH of coastal waters and points at opportunities to manage these trajectories locally to conserve coastal organisms vulnerable to ocean acidification.     

Network analysis to inform invasive species spread among lakes

Often facilitated by human-mediated pathways, aquatic invasive species are a threat to the health and biodiversity of global ecosystems. We present a novel approach incorporating survey data of watercraft movement in a social network analysis to reconstruct potential pathways of aquatic invasive species spread between lakes. As an example, we use the green alga Nitellopsis obtusa, also known as starry stonewort, an aquatic invasive species affecting the Great Lakes region in the United States and Canada. The movement of algal fragments via human-mediated pathways(i.e., watercraft) has been hypothesized as the primary driver of starry stonewort invasion. We used survey data collected at boat ramps during the 2013 and 2014 openwater seasons to describe the flow of watercraft from Lake Koronis, where N. obtusa was first detected in Minnesota, to other lakes in the state. Our results suggest that the risk of N. obtusa expansion is not highly constrained by geographic proximity and management efforts should consider highly connected lakes.Estimating human movement via network analysis may help to explain past and future routes of aquatic invasive species infestation between lakes and can improve evidence-based prevention and control efforts.     

Galactic clusters with associated Cepheid variables – VII. Berkeley 58 and CG Cassiopeiae

Photoelectric, photographic and CCD UBV photometry, spectroscopic observations and star counts are presented for the open cluster Berkeley 58 to examine a possible association with the 4.37 d Cepheid CG Cas. The cluster is difficult to separate from the early-type stars belonging to the Perseus spiral arm, in which it is located, but has reasonably well-defined parameters: an evolutionary age of ∼10⁸ yr, a mean reddening of   E ( B − V ) (B0) = 0.70 ± 0.03  s.e. and a distance of  3.03 ± 0.17 kpc ( V ₀− M _V = 12.40 ± 0.12  s.d.). CG Cas is a likely cluster coronal member on the basis of radial velocity, and its period increase of  +0.170 ± 0.014 s yr⁻¹  and large light amplitude describe a Cepheid in the third crossing of the instability strip lying slightly blueward of strip centre. Its inferred reddening and luminosity are   E ( B − V ) = 0.64 ± 0.02  s.e. and  〈 M _V 〉=−3.06 ± 0.12  . A possible K supergiant may also be a cluster member.     

Short Communication: Comments on Comparison of Seismic Dispersion and Attenuation Models by Ursin B. and Toverud T., Stud. Geophys. Geod., 46, 293-320

Studia Geophysica et Geodaetica -     

Measurement and analysis of currents along the Danish west coast

Summary Current meter records from summer and late fall at three positions have been analyzed and related to sea level and wind data. Spectral analysis shows that the most energetic fluctuations are due to tides with an amplitude corresponding to 0.2 m/s. The variability is mainly in the alongshore direction for tidal and subtidal frequencies. The adjusted sea level, which is decreasing northwards, has the strongest response for winds from land in the wintertime. In the summer a balance between bottom friction and alongshore wind stress is found with a resistance coefficient of 0.1 cm/s, while a more complicated balance exists in the winter. The mean flow during summer is about 2 cm/s. For an estimated length scale of 170 km this corresponds to an alongshore transport of 0.15·10⁶m³/s (=0.15 Sv).

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Strömungsmessungen und-analysen entlang der Dänischen Westküste

Zusammenfassung Strömungsmessungen im Sommer und im Herbst an drei Positionen wurden analysiert und in Beziehung zum Wasserstand und Windfeld gesetzt. Wie die Spektralanalyse zeigt, sind die energiereichsten Fluktuationen gezeitenbedingt mit einer Amplitude von 0,2 m/s. Die Variabilität ist am größten bei den Gezeiten- und Subgezeitenfrequenzen längs der Küste. Der sich einstellende Wasserstand, welcher nach Norden hin abnimmt, reagiert am stärksten bei ablandigen Winden im Winter. Im Sommer findet man ein Gleichgewicht zwischen Bodenreibung und küstenparallelen Windschub mit einem Reibungskoeffizient von 0,1 cm/s. Im Winter hingegen ist die Situation wesentlich komplizierter. Die mittlere Strömungsgeschwindigkeit beträgt ca. 2 cm/s im Sommer, das entspricht einem Transport von 0,15·10⁶ m³/s (=0,15 Sv) bei einer geschätzten Längenskala von 170 km.

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Mesures et analyse de courants le long de la côte danoise occidentale

Résumé Des données obtenues par courantmètres durant l'été et fin automne à trois sites sont analysées et comparées au niveau de la mer et aux vents. Une analyse spectrale montre que les fluctuations les plus énergétiques, avec des amplitudes de l'ordre de 0,2 m/s, sont attribuables aux marées. Leur variabilité est concentrée dans la direction parallèle à la côte pour les fréquences de marées es au-dessous. Après ajustement, le niveau de la mer, qui decroît vers le nord, réagit le plus fortement aux vents d'hiver dirigés au large. Pendant l'été, un équilibre entre la friction sur le fond et le cisailement du vent le long de la côte est atteint pour un coefficient de résistance de 0,1 cm/s, alors qu'un équilibre plus compliqué s'établit durant l'hiver. Le courant moyen pendant l'été est de l'ordre de 2 cm/s. Avec une longueur d'échelle estimée à 170 km, ceci correspond à un transport de 0,15·10⁶ m³/s (=0,15 Sv) le long de la côte.