Methods in Oceanography最新文献

A novel chemical sensor package named “WavepHOx” was developed in order to facilitate measurement of surface ocean pH, dissolved oxygen, and temperature from mobile platforms. The system comprises a Honeywell Durafet pH sensor, Aanderaa optode oxygen sensor, and chloride ion selective electrode, packaged into a hydrodynamic, lightweight housing. The WavepHOx has been deployed on a stand-up paddleboard and a Liquid Robotics Wave Glider in multiple near-shore settings in the Southern California Bight. Integration of the WavepHOx into these mobile platforms has enabled high spatiotemporal resolution pH and dissolved oxygen data collection. It is a particularly valuable tool for mapping shallow, fragile, or densely vegetated ecosystems which cannot be easily accessed by other platforms. Results from three surveys in San Diego, California, are reported. We show pH and dissolved oxygen variability >0.3 and >50% saturation, respectively, over tens to hundreds of meters to highlight the degree of natural spatial variability in these vegetated ecosystems. When deployed during an extensive discrete sampling program, the WavepHOx pH had a root mean squared error of 0.028 relative to pH calculated from fifty six measurements of total alkalinity and dissolved inorganic carbon, confirming its capacity for accurate, high spatiotemporal resolution data collection.

The contributions of autonomous underwater gliders as an observing platform in the in-situ global ocean observing system (GOOS) are investigated. The assessment is done in two ways: First, the existing in-situ observing platforms contributing to GOOS (floats, surface drifters, moorings, research/commercial ships) are characterized in terms of their current capabilities in sampling key physical and bio-geochemical oceanic processes. Next the gliders’ capabilities are evaluated in the context of key applications. This includes an evaluation of 140 references presented in the peer-reviewed literature.

It is found that GOOS has adequate coverage of sampling in the open ocean for several physical processes. There is a lack of data in the present GOOS in the transition regions between the open ocean and shelf seas. However, most of the documented scientific glider applications operate in this region, suggesting that a sustained glider component in the GOOS could fill that gap. Glider data are included for routine product generation (e.g. alerts, maps). Other noteworthy process-oriented applications where gliders are important survey tools include local sampling of the (sub)mesoscale, sampling in shallow coastal areas, measurements in hazardous environments, and operational monitoring. In most cases, the glider studies address investigations and monitoring of processes across multiple disciplines, making use of the ease to implement a wide range of sensors to gliders. The maturity of glider operations, the wide range of applications that map onto growing GOOS regional needs, and the maturity of glider data flow all justify the formal implementation of gliders into the GOOS. Remaining challenges include the execution of coordinated multinational missions in a sustained mode as well as considering capacity-building aspects in glider operations as well as glider data use.

We quantify the percentage of sea surface covered by whitecaps from images taken by a non-stationary camera mounted on a moored buoy using an Adaptive Thresholding Segmentation (ATS) method and an Iterative Between Class Variance (IBCV) approach. In the ATS algorithm, the optimal value for the threshold is determined as the last inflection point of the smoothed cumulative histogram of the scene. This makes the method more effective in finding the optimal value of the threshold and reduces the computational efforts compared to the conventional Automated Whitecap Extraction (AWE) technique. In the IBCV method, the optimum criterion for determining the value of the threshold corresponds to the measure of separability between the segmented water and whitecap pixels. In our experiments, the fraction of each image covered by the whitecap is determined using the aforementioned dynamical thresholding techniques for images taken under complex forcing and lighting conditions. Comparisons between different techniques suggest the effectiveness of the proposed methodologies, in particular the ATS algorithm to separate the whitecap features from the darker water pixels.

3D printers allow researchers to produce parts and concept models rapidly at low-cost and allow rapid prototyping of many designs from the comfort of their desk. 3D printing technologies have been explored for a wide range of applications including robotics, automobile components, firearms, medicine, space, etc. Owing to lower costs and increased capabilities of 3D printing technologies, unprecedented opportunities in the world of oceanography research are being created. Some examples include 3D printed components being employed in autonomous underwater (or surface) vehicles; 3D printed replicas of marine organisms being used to study biomechanics, hydrodynamics, and locomotion; and 3D printed coral reef replicas being used to restore damaged coral reefs. To the author’s knowledge, currently there is no review covering the different 3D printing technologies applied in oceanography studies. Therefore, this review presents a summary of the different 3D printing technologies that have been used in fundamental studies or real-life applications related to oceanography. The diverse range of 3D printing applications in oceanography covered in this review has been categorized under the following sub-topics: Ecological Monitoring & Sample Collection, Hydrodynamics, Biomechanics & Locomotion, Tracking & Surface Studies, and Tangible Coral Props & Coral Reef Restoration. A detailed overview of the 3D printing technologies referred to within this review has been presented, and categorized under the following four general topics: Material Extrusion, Photopolymerization, Powder Bed Fusion, and Construction Printing. The broad impact of plastics on oceans and the specific impact of 3D printing materials on ocean life are also discussed. It is anticipated that this review will further promote the 3D printing technologies to oceanographers for a better understanding and restoration of fragile marine ecosystems.

The Sea is often a fragile environment to be protected against possible pollutants. In this context, the present work contributes to its safeguard by proposing a new buoy equipped with advanced sensors for the detection of oil spills. In particular, the buoy is provided with various sensors for the evaluation of both meteorological and marine parameters (e.g. waves, wind, temperature), and chemical/physical data acquired by an electronic nose system specifically designed for the detection of hydrocarbons. The electronic nose is composed of a flow chamber, a chamber equipped with photo ionization sensors, pumps and valves for air inlet and outlet, and a low-cost electronic board. The designed system samples the air above the water and produces data that are processed through two artificial neural networks allowing for a classification of detected hydrocarbons and overall pollution level. Suitable network interfaces and a connector toward a Marine Information System (MIS) allow both for real-time data visualization and for long-term assessment of water quality.

Understanding intrusive exchange at oceanic water mass fronts may depend on building data-constrained models of the processes, but obtaining the needed representative and comprehensive data is challenging. Acoustic imaging (remote sensing) is an attractive method for mapping the three-dimensional intrusion geometry to enable the required focused in situ sampling of the mixing processes in intrusions. The method depends on backscatter of sound from sharp interfaces and from microstructure resulting from double-diffusive instability (DDI), a probable occurrence at intrusions. The potential of the method is evaluated using data collected using established methods in a field of intrusions south of New England. Above and beneath warm and salty intrusions may lie diffusive–convective DDI microstructure and salt-fingering microstructure, respectively, marking the intrusion boundaries, providing the backscattering features. The data show that both types of microstructure can occur in close proximity within intrusions, but the question of whether this is common or not is unanswered by the modest amount of data, as are questions about continuity of DDI-microstructure in intrusions (to facilitate intrusion acoustic imaging) and variability of DDI-driven heat, salt and buoyancy fluxes. Analysis here shows that detectable backscatter from DDI-microstructure will occur, and can be easily measured when plankton scattering is low enough. Interface scattering is also likely to be detectable. The DDI-linked microstructure data used here are inherently interesting in their own right and are presented in some detail.

Incident shortwave solar radiation entering the ocean depends on albedo $\alpha$ and plays an important role in the temperature variability and pathogen mortality of the nearshore region. As foam has an elevated albedo, open-ocean albedo parameterizations include whitecapping effects through a wind-based foam fraction. However, surfzone depth-limited wave breaking does not require wind. Surfzone albedo observations are very rare, the variability of surfzone albedo is not known, and parameterizations are not available. New, year-long upwelling and downwelling shortwave radiation observations were made from the Scripps Institution of Oceanography pier spanning the surfzone and inner-shelf. Surfzone albedo was elevated due to foam with mean observed albedo of $\alpha =0.15$ and one-minute average albedo as high as $\alpha =0.45$, far exceeding expected albedo (0.06) from standard parameterizations. Using a pier-mounted GoPro camera, an image-based albedo parameterization is developed that estimates the fractional foam area to derive albedo. This parameterization has high skill ($r^2=0.90$) on time scales as short as a wave period (9 s). A second wave-model based parameterization for (hourly) averaged albedo is developed relating the non-dimensional roller energy dissipation to the mean foam fraction and thus albedo. The parameterization has good skill ($r^2=0.68$) and resolves cross-shore albedo variations. These new parameterizations can be used where imagery is available or wave models are applicable, and can be used to constrain local heat budgets and pathogen mortality.

The suitability of the colorimetric method in a custom-made instrumental set-up and the commercial potentiometric SeaFET^®electrode sensor to measure pH in surface oceanic water in the Arctic was investigated during the Chinese Arctic Research Expedition (CHINARE) in summer 2014. The instruments were set up in parallel on the on-board underway seawater supply for 65 days, enabling comparison in various conditions in the Arctic Ocean from the Chukchi Sea to the ice-covered high latitudes (81^°N) and the open-water North-western Pacific Ocean. Overall, the instruments yielded pH datasets of similar high quality (method uncertainty $\le 0.010$). Detailed comparison with the parallel colorimetric pH measurements indicated that the measurements with the SeaFET external electrode in the low salinity ice-covered area were problematical and that the internal reference electrode failed after almost 2 months of cruise. Reasons for discrepancies between the data from the two instruments and recommendations for the use of either instrument for pH measurements in the Arctic are discussed. Finally, the investigation yielded a reliable high-resolution pH dataset in surface waters along a transect from the Pacific to the Arctic Ocean. Large pH variations were observed in the ice-free Arctic surface waters, with pH ranging between 7.98 and 8.49. The highest pH values were observed at the ice edge, whereas a relatively invariable pH ($8.02\pm 0.02$) was measured in under-ice seawater in the ice-covered Arctic Ocean. The high resolution surface seawater pH dataset obtained here could be used as reference to detect the on-going acidification rate in the Pacific Arctic.

In most aquatic environments, suspended sediment is composed of loosely packed particle aggregates, termed flocs that have variable apparent densities. The apparent density of flocs, which is defined as particle dry mass over wet volume, is an important variable because it affects settling velocity and vertical sediment flux. Two established methods exist for measuring apparent density. One method uses physical measurements of sediment mass concentration combined with measurements of particle volume concentration from optical instruments to estimate apparent density. This method is laborious because it requires the collection of water samples, so it is not conducive to construction of high-resolution time series of density. Another method uses video observations of particles in a settling column to measure particle size and settling velocity. These measurements are used to solve for apparent density according to Stokes Law. The goal of this study is to develop a new method that uses the ratio of particulate beam attenuation to particle volume to estimate apparent density of sediment in suspension. Data from five studies are used to compare density estimates with the new method to the previous methods. The new optical method produces apparent densities that are correlated linearly with measurements of the ratio of dry mass to wet volume. However, the new optical method produces density estimates that do not correlate with video estimates of apparent density. This lack of correlation is due to sampling bias of the video method, which has a relatively large lower limit of resolution in particle size. Development of a higher resolution camera would eliminate the current bias in particle size and would enable further assessment of the new optical method as an accurate proxy for apparent density.

Near-surface chlorophyll $a$ concentration is a fundamental component of marine ecological processes, and its changes reflect the phytoplankton growth (primary productivity as well as loss due to grazing and sinking) feeding into higher trophic levels. Time series of measurements from several satellite sensors since late 1997 can be used as a proxy of chlorophyll $a$ concentrations after calibrating against direct sea water measurements from oceanographic surveys. Previous studies indicate a need for a regional correction model in specific ‘case 2’ areas, where the relationship between satellite measurements and in situ measurements is different from the relationship in the general ‘case 1’ areas, due to complex environmental characteristics in different areas. Subarctic and boreal North Atlantic, including the waters around Iceland, have been considered case 2 waters, but a regional correction model has not been developed until now. We collated all relevant measurements of near-surface chlorophyll $a$ from sea water samples, available in the Marine Research Institute database, and matched by date and location with satellite chlorophyll records, i.e. the GSM CHL1 records offered by the GlobColour Project. A multiple linear regression model was fitted to the observed in situ chlorophyll measurements, based on the satellite chlorophyll values (CHL1) and physical covariates: day of the year, sun elevation, and ocean depth. The resulting parsimonious model converts the satellite measurements to estimates that are in much better agreement with in situ measurements ($R^2$ increases from 0.2 to 0.5), and is therefore proposed for calibration of regional corrections to the GlobColour Project’s GSM chlorophyll parameter, CHL1.