Applied Ocean Physics and Engineering (AOP&E)
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The Department is a major center for research in fluid mechanics, coastal processes, ocean mixing, acoustics, air-sea interaction, deep submergence, ocean systems and moorings, remote sensing, robotics, certain biological processes, image processing, signal processing and estimation, control theory, and the dynamics of ocean cables.
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ArticleBroadening inclusivity at sea(Frontiers Media, 2024-06-13)Ocean sciences in the U.S. remains a field with one of the lowest rates of diversity, having disproportionately low representation from marginalized groups, including Black, Asian, LatinX, Indigenous, and other people of color; LGBTQIA+ individuals; disabled persons; women; those with neurological differences; and those from low-income groups. With equity and inclusion in mind, recent efforts have been made to increase the number of ocean science professionals from marginalized groups through multiple entry points, including internships. However, there still exists a large gap between the diversity found in the general population and the diversity within ocean sciences. Perhaps one reason why this field continues to have lower diversity owes to the unique component of many oceanographic careers, which continues to present an especially high barrier for marginalized groups: participating in sea-going research expeditions. Herein, we have synthesized possible ways to prioritize the physical and emotional safety of marginalized ocean science professionals participating in a research expedition, including guidance on preparation, implementation, and providing support post-cruise. These suggestions are intended to be useful for the broader oceanographic research community to consider the safety and well-being of individuals from marginalized groups at sea, since the field of ocean sciences - like all fields - would greatly benefit from increased representation and diversity.
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ArticleImpacts of hydrostatic pressure on distributed temperature-sensing optical fibers for extreme ocean and ice environments(MDPI, 2024-07-02)Optical fiber is increasingly used for both communication and distributed sensing of temperature and strain in environmental studies. In this work, we demonstrate the viability of unreinforced fiber tethers (bare fiber) for Raman-based distributed temperature sensing in deep ocean and deep ice environments. High-pressure testing of single-mode and multimode optical fiber showed little to no changes in light attenuation over pressures from atmospheric to 600 bars. Most importantly, the differential attenuation between Stokes and anti-Stokes frequencies, critical for the evaluation of distributed temperature sensing, was shown to be insignificantly affected by fluid pressures over the range of pressures tested for single-mode fiber, and only very slightly affected in multimode fiber. For multimode fiber deployments to ocean depths as great as 6000 m, the effect of pressure-dependent differential attenuation was shown to impact the estimated temperatures by only 0.15 °K. These new results indicate that bare fiber tethers, in addition to use for communication, can be used for distributed temperature or strain in fibers subjected to large depth (pressure) in varying environments such as deep oceans, glaciers and potentially the icy moons of Saturn and Jupiter.
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ArticleHarnessing (geoacoustic) uncertainty(Acoustical Society of America, 2024-07-01)In 1979, in his The Hitchhiker's Guide to the Galaxy,1 Douglas Adams wrote, “we demand rigidly defined areas of doubt and uncertainty!” In a 2002 article in the Journal of the Acoustical Society of America, Stan Dosso delivered an impactful solution2 for geoacoustic inversion.
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ArticleOptimizing seaweed biomass production—A two kelp solution(Springer, 2024-07-02)Interest in farming kelps has grown beyond using kelp for food, feed or biofuels. There is considerable interest in generating biomass from seaweed for use in bioplastics and other products that would substitute for petroleum-derived products. For these uses to be viable, large amounts of biomass are needed. Very large kelp farms can be expensive to build and maintain, leading to the need to optimize the biomass per unit area. Although close spacing of growlines can lead to poor growth, a viable approach may be to grow two species of kelps together: one that hangs down and one that is buoyant, growing up. This system would increase the spacing in three dimensions. In Alaska, Saccharina latissima is commonly grown hanging down from longlines. One of the buoyant Alaskan kelps is Nereocystis luetkeana. Because there are commercial uses for wild-harvested Nereocystis in Alaska, we undertook a preliminary trial in Kodiak, Alaska, that grew both Saccharina and Nereocystis in the same longline array. Closely spaced lines were seeded the first week of February 2023 and set at 3 m below the surface. The arrays were harvested in late June 2023. Total yields were greatest on the combined arrays, followed by the Nereocystis only and Saccharina only arrays. Despite having 45% fewer grow-lines, the total yield of the Nereocystis on the combined arrays was statistically similar to the Nereocystis only arrays. These results may have significance for large scale macroalgal production.
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ArticleOn the role of small estuaries in retaining buoyant particles(National Academy of Sciences, 2024-08-19)Estuaries, as connectors between land and ocean, have complex interactions of river and tidal flows that affect the transport of buoyant materials like floating plastics, oil spills, organic matter, and larvae. This study investigates surface-trapped buoyant particle transport in estuaries by using idealized and realistic numerical simulations along with a theoretical model. While river discharge and estuarine exchange flow are usually expected to export buoyant particles to the ocean over subtidal timescales, this study reveals a ubiquitous physical transport mechanism that causes retention of buoyant particles in estuaries. Tidally varying surface convergence fronts affect the aggregation of buoyant particles, and the coupling between particle aggregation and oscillatory tidal currents leads to landward transport at subtidal timescales. Landward transport and retention of buoyant particles is greater in small estuaries, while large estuaries tend to export buoyant particles to the ocean. A dimensionless width parameter incorporating the tidal radian frequency and lateral velocity distinguishes small and large estuaries at a transitional value of around 1. Additionally, higher river flow tends to shift estuaries toward seaward transport and export of buoyant particles. These findings provide insights into understanding the distribution of buoyant materials in estuaries and predicting their fate in the land–sea exchange processes.
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ArticleSea ice mass balance during the MOSAiC drift experiment: Results from manual ice and snow thickness gauges(University of California Press, 2024-07-09)Precise measurements of Arctic sea ice mass balance are necessary to understand the rapidly changing sea ice cover and its representation in climate models. During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we made repeat point measurements of snow and ice thickness on primarily level first- and second-year ice (FYI, SYI) using ablation stakes and ice thickness gauges. This technique enabled us to distinguish surface and bottom (basal) melt and characterize the importance of oceanic versus atmospheric forcing. We also evaluated the time series of ice growth and melt in the context of other MOSAiC observations and historical mass balance observations from the Surface Heat Budget of the Arctic (SHEBA) campaign and the North Pole Environmental Observatory (NPEO). Despite similar freezing degree days, average ice growth at MOSAiC was greater on FYI (1.67 m) and SYI (1.23 m) than at SHEBA (1.45 m, 0.53 m), due in part to initially thinner ice and snow conditions on MOSAiC. Our estimates of effective snow thermal conductivity, which agree with SHEBA results and other MOSAiC observations, are unlikely to explain the difference. On MOSAiC, FYI grew more and faster than SYI, demonstrating a feedback loop that acts to increase ice production after multi-year ice loss. Surface melt on MOSAiC (mean of 0.50 m) was greater than at NPEO (0.18 m), with considerable spatial variability that correlated with surface albedo variability. Basal melt was relatively small (mean of 0.12 m), and higher than NPEO observations (0.07 m). Finally, we present observations showing that false bottoms reduced basal melt rates in some FYI cases, in agreement with other observations at MOSAiC. These detailed mass balance observations will allow further investigation into connections between the carefully observed surface energy budget, ocean heat fluxes, sea ice, and ecosystem at MOSAiC and during other campaigns.
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ArticleA shared autonomy system for precise and efficient remote underwater manipulation(Institute of Electrical and Electronics Engineers, 2024-07-22)Conventional underwater intervention operations using robotic vehicles require expert teleoperators and limit interaction with remote scientists. In this article, we present the shared autonomy for remote collaboration (SHARC) framework that enables novice operators to cooperatively conduct underwater sampling and manipulation tasks. With SHARC, operators can plan and complete manipulation tasks using natural language or hand gestures through a virtual reality (SHARC-VR) interface. The interface provides remote operators with a contextual 3-D scene understanding that is updated according to bandwidth availability. Evaluation of the SHARC framework through controlled lab experiments demonstrates that SHARC-VR enables novice operators to complete manipulation tasks in framerate-limited conditions (i.e., 0.1–0.5 frames per second) faster than expert pilots using a conventional topside controller. For both novice and expert users, the SHARC-VR interface also increases the task completion rate and improves sampling precision. The SHARC framework is readily extensible to other hardware architectures, including terrestrial and space systems.
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ArticleA numerical investigation on the vibration of a two-deck euler–bernoulli beam flooded by a potential flow(Oxford University Press, 2024-05-28)This work concerns the structural vibration of a bladeless wind turbine, modelled by a two-deck Euler–Bernoulli beam, due to a surrounding potential flow. The deflection is governed by the Euler–Bernoulli equation which is studied first by a linear theory and then computed numerically by a finite difference method in space with a collocation method over the arc length, and an implicit Euler method in time. The fluid motion in the presence of gravity is governed by the full Euler equations and solved by the time-dependent conformal mapping technique together with a pseudo-spectral method. Numerical experiments of excitation by a moving disturbance on the fluid surface with/without a stochastic noise are carried out. The random process involved in generating the noise on the water surface is driven by a Wiener Process. A Monte Carlo method is used for stochastic computations. The generated surface waves impinge on the beam causing structural vibration which is presented and discussed in detail. By elementary statistical analysis, the structural response subject to the stochastic hydrodynamic disturbance caused by white noise is found to be Gaussian.
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ArticleUpwelling in cyclonic and anticyclonic eddies at the Middle Atlantic Bight shelf-break front(American Geophysical Union, 2024-08-10)Despite the ubiquity of eddies at the Mid-Atlantic Bight shelf-break front, direct observations of frontal eddies at the shelf-break front are historically sparse and their biological impact is mostly unknown. This study combines high resolution physical and biological snapshots of two frontal eddies with an idealized 3-D regional model to investigate eddy formation, kinematics, upwelling patterns, and biological impacts. During May 2019, two eddies were observed in situ at the shelf-break front. Each eddy showed evidence of nutrient and chlorophyll enhancement despite rotating in opposite directions and having different physical characteristics. Our results suggest that cyclonic eddies form as shelf waters are advected offshore and slope waters are advected shoreward, forming two filaments that spiral inward until sufficient water is entrained. Rising isohalines and upwelled slope water dye tracer within the model suggest that upwelling coincided with eddy formation and persisted for the duration of the eddy. In contrast, anticyclonic eddies form within troughs of the meandering shelf-break front, with amplified frontal meanders creating recirculating flow. Upwelling of subsurface shelf water occurs in the form of detached cold pool waters during the formation of the anticyclonic eddies. The stability properties of each eddy type were estimated via the Burger number and suggest different ratios of baroclinic versus barotropic contributions to frontal eddy formation. Our observations and model results indicate that both eddy types may persist for more than a month and upwelling in both eddy types may have significant impacts on biological productivity of the shelf break.
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ArticleSynchronicity of the Gulf Stream path downstream of Cape Hatteras and the region of maximum wind stress curl(Nature Research, 2024-08-09)The Gulf Stream, a major ocean current in the North Atlantic ocean is a key component in the global redistribution of heat and is important for marine ecosystems. Based on 27 years (1993–2019) of wind reanalysis and satellite altimetry measurements, we present observational evidence that the path of this freely meandering jet after its separation from the continental slope at Cape Hatteras, aligns with the region of maximum cyclonic vorticity of the wind stress field known as the positive vorticity pool. This synchronicity between the wind stress curl maximum region and the Gulf Stream path is observed at multiple time-scales ranging from months to decades, spanning a distance of 1500 km between 70 and 55W. The wind stress curl in the positive vorticity pool is estimated to drive persistent upward vertical velocities ranging from 5 to 17 cm day−1 over its ~ 400,000 km2 area; this upwelling may supply a steady source of deep nutrients to the Slope Sea region, and can explain as much as a quarter of estimated primary productivity there.
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ArticleVegetation-generated turbulence does not impact the erosion of natural cohesive sediment(American Geophysical Union, 2024-07-10)Previous studies have demonstrated that vegetation-generated turbulence can enhance erosion rate and reduce the velocity threshold for erosion of non-cohesive sediment. This study considered whether vegetation-generated turbulence had a similar influence on natural cohesive sediment. Cores were collected from a black mangrove forest with aboveground biomass and exposed to stepwise increases in velocity. Erosion was recorded through suspended sediment concentration. For the same velocity, cores with pneumatophores had elevated turbulent kinetic energy compared to bare cores without pneumatophores. However, the vegetation-generated turbulence did not increase bed stress or the rate of resuspension, relative to bare cores. It was hypothesized that the short time-scale fluctuations associated with vegetation-generated turbulence were not of sufficient duration to break cohesion between grains, explaining why elevated levels of turbulence associated with the pneumatophores had no impact on the erosion threshold or rate.
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ArticlePlanned Geological Investigations of the Europa Clipper Mission(Springer, 2024-02-12)Geological investigations planned for the Europa Clipper mission will examine the formation, evolution, and expression of geomorphic structures found on the surface. Understanding geologic features, their formation, and any recent activity are key inputs in constraining Europa’s potential for habitability. In addition to providing information about the moon’s habitability, the geologic study of Europa is compelling in and of itself. Here we provide a high-level, cross-instrument, and cross-discipline overview of the geologic investigations planned within the Europa Clipper mission. Europa’s fascinating collection of ice-focused geology provides an unparalleled opportunity to investigate the dynamics of icy shells, ice-ocean exchange processes, and global-scale tectonic and tidal stresses. We present an overview of what is currently known about the geology of Europa, from global to local scales, highlighting outstanding issues and open questions, and detailing how the Europa Clipper mission will address them. We describe the mission’s strategy for searching for and characterizing current activity in the form of possible active plumes, thermal anomalies, evidence for surface changes, and extremely fresh surface exposures. The complementary and synergistic nature of the data sets from the various instruments and their integration will be key to significantly advancing our understanding of Europa’s geology.
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ArticleExploring the role of wave-driven turbulence at the air-sea interface through measurements of TKE dissipation rates across the air-sea interface(American Geophysical Union, 2024-08-16)This work serves as an observation-based exploration into the role of wave-driven turbulence at the air-sea interface by measuring Turbulent Kinetic Energy (TKE) dissipation rates above and below the sea surface. Subsurface ocean measurements confirm a TKE dissipation rate enhancement relative to the predicted law-of-the-wall (εobs > εp), which appears to be fully supported by wave breaking highlighting the role of the transport terms in balancing the subsurface TKE budget. Simultaneous measurements of TKE dissipation rates on the atmospheric side capture a deficit relative to the law-of-the-wall (εobs < εp). This deficit is explained in terms of wave-induced perturbations, with observed convergence to the law-of-the-wall at 14 m above mean sea level. The deficit on the atmospheric side provides an estimate of the energy flux divergence in the wave boundary layer. An exponential function is used to integrate in the vertical and provide novel estimates of the amount of energy going into the wave field. These estimates correlate well with classic spectral input parameterizations and can be used to derive an effective wave-scale, capturing wind-wave coupling purely from atmospheric observations intimately tied to wave-induced perturbations of the air-flow. These atmospheric and oceanic observations corroborate the commonly assumed input-dissipation balance for waves at wind speeds in the 8-14 ms−1 range in the presence of developed to young seas. At wind speeds above 14 ms−1 under young seas (U10/cp > 1.2)observations suggest a deviation from the TKE input-dissipation balance in the wave field.
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ArticleFrom shelfbreak to shoreline: coastal sea level and local ocean dynamics in the Northwest Atlantic(American Geophysical Union, 2024-07-19)Sea-level change threatens the U.S. East Coast. Thus, it is important to understand the underlying causes, including ocean dynamics. Most past studies emphasized links between coastal sea level and local atmospheric variability or large-scale circulation and climate, but possible relationships with local ocean currents over the shelf and slope remain largely unexplored. Here we use 7 years of in situ velocity and sea-level data to quantify the relationship between northeastern U.S. coastal sea level and variable Shelfbreak Jet transport south of Nantucket Island. At timescales of 1–15 days, southern New England coastal sea level and transport vary in anti-phase, with magnitude-squared coherences of ∼0.5 and admittance amplitudes of ∼0.3 m Sv−1. These results are consistent with a dominant geostrophic balance between along-shelf transport and coastal sea level, corroborating a hypothesis made decades ago that was not tested due to the lack of transport data.
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ArticleRemote sensing of emperor penguin abundance and breeding success(Nature Research, 2024-05-29)Emperor penguins (Aptenodytes forsteri) are under increasing environmental pressure. Monitoring colony size and population trends of this Antarctic seabird relies primarily on satellite imagery recorded near the end of the breeding season, when light conditions levels are sufficient to capture images, but colony occupancy is highly variable. To correct population estimates for this variability, we develop a phenological model that can predict the number of breeding pairs and fledging chicks, as well as key phenological events such as arrival, hatching and foraging times, from as few as six data points from a single season. The ability to extrapolate occupancy from sparse data makes the model particularly useful for monitoring remotely sensed animal colonies where ground-based population estimates are rare or unavailable.
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ArticleDevelopment of a quantum cascade laser absorption spectrometer for simultaneous measurement of 13C-18O and 18O-18O clumping in CO2(Wiley, 2024-06-18)Dual clumped isotope paleothermometry determines carbonate formation temperatures by measuring the frequency of 13C–18O (∆638) and 18O–18O (∆828) pairs in carbonates. It resolves isotopic kinetic biases and thus enables more accurate paleotemperature reconstructions. However, high-precision measurements of 18O–18O clumping using current techniques requires large sample sizes and long acquisition times. We developed a mid-infrared isotope ratio laser spectrometer (IRLS) for simultaneous measurement of the isotopologue ratios ∆638 and ∆828 in gas-phase carbon dioxide (CO2) at room temperature. Our IRLS uses a single laser scanning from 2290.7 to 2291.1 cm−1 and a 31 m pathlength optical cell, and it simultaneously measures the five isotopologues required for calculating ∆638 and ∆828: 16O12C16O, 16O13C16O, 16O12C18O, 16O13C18O, and 18O12C18O. In addition, our IRLS can measure 16O12C17O, enabling ∆17O analysis. At ~20°C and a CO2 pressure of ~2 Torr, our IRLS system achieved precisions of 0.128‰ and 0.140‰ within 20 s for abundances of the clumped isotopologues 16O13C18O and 18O12C18O, respectively, and precisions of 0.267‰, 0.245‰, and 0.128‰ for 16O12C16O, 16O13C16O, and 16O12C18O. This yielded precisions of 0.348‰ (∆638) and 0.302‰ (∆828) within 25 s. Simulated sample–reference switching highlights the potential of our system and the need for further development. We demonstrated simultaneous measurements of ∆638 and ∆828 in CO2 to precisions of <0.35‰ within 25 s using a room-temperature, single-laser IRLS. Future developments on better resolving 16O12C16O and 16O13C16O peaks and system temperature control could further improve the measurement precision.
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ArticleA new framework for quantifying alongshore variability of swash motion using fully convolutional networks(Elsevier, 2024-05-24)Waves running up and down the beach (‘swash’) at the landward edge of the ocean can cause changes to the beach topology, can erode dunes, and can result in inland flooding. Despite the importance of swash, field observations are difficult to obtain in the thin, bubbly, and potentially sediment laden fluid layers. Here, swash excursions along an Atlantic Ocean beach are estimated with a new framework, V-BeachNet, that uses a fully convolutional network to distinguish between sand and the moving edge of the wave in rapid sequences of images. V-BeachNet is trained with 16 randomly selected and manually segmented images of the swash zone, and is used to estimate swash excursions along 200 m of the shoreline by automatically segmenting four 1-h sequences of images that span a range of incident wave conditions. Data from a scanning lidar system are used to validate the swash estimates along a cross-shore transect within the camera field of view. V-BeachNet estimates of swash spectra, significant wave heights, and wave-driven setup (increases in the mean water level) agree with those estimated from the lidar data.
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ArticleOcean surface radiation measurement best practices(Frontiers Media, 2024-05-23)Ocean surface radiation measurement best practices have been developed as a first step to support the interoperability of radiation measurements across multiple ocean platforms and between land and ocean networks. This document describes the consensus by a working group of radiation measurement experts from land, ocean, and aircraft communities. The scope was limited to broadband shortwave (solar) and longwave (terrestrial infrared) surface irradiance measurements for quantification of the surface radiation budget. Best practices for spectral measurements for biological purposes like photosynthetically active radiation and ocean color are only mentioned briefly to motivate future interactions between the physical surface flux and biological radiation measurement communities. Topics discussed in these best practices include instrument selection, handling of sensors and installation, data quality monitoring, data processing, and calibration. It is recognized that platform and resource limitations may prohibit incorporating all best practices into all measurements and that spatial coverage is also an important motivator for expanding current networks. Thus, one of the key recommendations is to perform interoperability experiments that can help quantify the uncertainty of different practices and lay the groundwork for a multi-tiered global network with a mix of high-accuracy reference stations and lower-cost platforms and practices that can fill in spatial gaps.
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ArticleThe MOSAiC Distributed Network: Observing the coupled Arctic system with multidisciplinary, coordinated platforms(University of California Press, 2024-05-10)Central Arctic properties and processes are important to the regional and global coupled climate system. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Distributed Network (DN) of autonomous ice-tethered systems aimed to bridge gaps in our understanding of temporal and spatial scales, in particular with respect to the resolution of Earth system models. By characterizing variability around local measurements made at a Central Observatory, the DN covers both the coupled system interactions involving the ocean-ice-atmosphere interfaces as well as three-dimensional processes in the ocean, sea ice, and atmosphere. The more than 200 autonomous instruments (“buoys”) were of varying complexity and set up at different sites mostly within 50 km of the Central Observatory. During an exemplary midwinter month, the DN observations captured the spatial variability of atmospheric processes on sub-monthly time scales, but less so for monthly means. They show significant variability in snow depth and ice thickness, and provide a temporally and spatially resolved characterization of ice motion and deformation, showing coherency at the DN scale but less at smaller spatial scales. Ocean data show the background gradient across the DN as well as spatially dependent time variability due to local mixed layer sub-mesoscale and mesoscale processes, influenced by a variable ice cover. The second case (May–June 2020) illustrates the utility of the DN during the absence of manually obtained data by providing continuity of physical and biological observations during this key transitional period. We show examples of synergies between the extensive MOSAiC remote sensing observations and numerical modeling, such as estimating the skill of ice drift forecasts and evaluating coupled system modeling. The MOSAiC DN has been proven to enable analysis of local to mesoscale processes in the coupled atmosphere-ice-ocean system and has the potential to improve model parameterizations of important, unresolved processes in the future.
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ArticleDevelopment of single-pin, un-barbed, pole-tagging of free-swimming dolphins and sharks with satellite-linked transmitters(BioMed Central, 2024-04-15)To tag large marine vertebrates, without the need to catch them, avoiding using barbs for tag retention, and precisely controlling tag location, the remote Tag Attachment Device on a pole (TADpole) was developed. This allows single-pin tags (Finmount, Wildlife Computers) to be attached to the dorsal fins of free-swimming large marine vertebrates.