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Andrey Shcherbina Principal Oceanographer Affiliate Assistant Professor, Civil and Environmental Engineering ashcherbina@apl.washington.edu Phone 206-897-1446 |
Education
M.S. Physical Oceanography, Moscow Institute of Physics and Technology, 1998
Ph.D. Physical Oceanography, Scripps Institution of Oceanography, 2004
Projects
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Salinity Processes in the Upper Ocean Regional Study SPURS The NASA SPURS research effort is actively addressing the essential role of the ocean in the global water cycle by measuring salinity and accumulating other data to improve our basic understanding of the ocean's water cycle and its ties to climate. |
15 Apr 2015
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Lateral Mixing Small scale eddies and internal waves in the ocean mix water masses laterally, as well as vertically. This multi-investigator project aims to study the physics of this mixing by combining dye dispersion studies with detailed measurements of the velocity, temperature and salinity field during field experiments in 2011 and 2012. |
1 Sep 2012
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APL-UW Involvement in the Coastal Margin Observation and Prediction Science and Technology Center (CMOP) AUVs will be deployed by a newly formed APL-UW AUV group as part of CMOP's experimental observation network which consists of multiple fixed and mobile platforms equipped with oceanographic sensors. |
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15 Jun 2012
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The Center for Coastal Margin Observation and Predication (CMOP) has purchased from Hydroid, LLC two Autonomous Underwater Vehicles (AUVs) for its studies. The REMUS (Remote Environmental Measuring Units) 100 (see Figure 1) is a compact, light-weight, AUV designed for operation in coastal environments up to 100 meters in depth. The AUVs will be deployed by a newly formed APL-UW AUV group as part of CMOP's experimental observation network which consists of multiple fixed and mobile platforms equipped with oceanographic sensors. The AUVs will be used, primarily, to study the Columbia River plume and estuary region. The AUVs will be deployed periodically throughout each operational year. We also plan to allow customization of the AUVs by integrating novel biogeochemical sensors to meet specific scientific objectives for the CMOP program. |
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Intrusions in the North Pacific Subtropical Frontal Zone A field study of the interleaving features in the Subtropical Frontal Zone (STFZ) of the North Pacific Ocean was conducted from in July 2007. The experiment encompassed hydrographic surveying with a towed depth-cycling conductivity-temperature-depth (CTD) platform SWIMS, microstructure profiling, shipboard velocity observations, and |
6 Apr 2011
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Videos
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Lagrangian Submesoscale Experiment LASER A science team led by Eric D'Asaro conducted a unique mission to deploy over 1,000 ocean drifters in a small area of the Gulf of Mexico. The real-time data collected from the biodegradable drifters recalibrated understanding of ocean currents. |
22 Jan 2018
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Publications |
2000-present and while at APL-UW |
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Diagnosing frontal dynamics from observations using a variational approach Cutolo, E., and 11 others including A. Shcherbina and E. D'Asaro, "Diagnosing frontal dynamics from observations using a variational approach," J. Geophys. Res., 127, doi:10.1029/2021JC018336, 2022. |
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1 Nov 2022 ![]() |
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Intensive hydrographic and horizontal velocity measurements collected in the Alboran Sea enabled us to diagnose the three-dimensional dynamics of a frontal system. The sampled domain was characterized by a 40 km diameter anticyclonic eddy, with an intense front on its eastern side, separating the Atlantic and Mediterranean waters. Here, we implemented a multi-variate variational analysis (VA) to reconstruct the hydrographic fields, combining the 1-km horizontal resolution of the Underway Conductivity-Temperature-Depth (CTD) system with information on the flow shape from the Acoustic Doppler Current Profiler velocities. One advantage of the VA is given by the physical constraint, which preserves fine-scale gradients better than the classical optimal interpolation (OI). A comparison between real drifter trajectories and virtual particles advected in the mapping quantified the improvements in the VA over the OI, with a 15% larger skill score. Quasi-geostrophic (QG) and semi-geostrophic (SG) omega equations enabled us to estimate the vertical velocity (w) which reached 40 m/day on the dense side of the front. How nutrients and other passive tracers leave the mixed-layer and subduct is estimated with 3D advection from the VA, which agreed with biological sampling from traditional CTD casts at two eddy locations. Downwelling warm filaments are further evidence of subduction, in line with the w from SG, but not with QG. SG better accounted for the along-isopycnal component of w in agreement with another analysis made on isopycnal coordinates. The multi-platform approach of this work and the use of variational methods improved the characterization and understanding of (sub)-mesoscale frontal dynamics. |
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Emergence of a neopelagic community through the establishment of coastal species on the high seas Haram, L.E., and 10 others including A.Y. Shcherbina, "Emergence of a neopelagic community through the establishment of coastal species on the high seas," Nat. Commun., 12, doi:10.1038/s41467-021-27188-6, 2021. |
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2 Dec 2021 ![]() |
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Discoveries of persistent coastal species in the open ocean shift our understanding of biogeographic barriers. Floating plastic debris from pollution now supports a novel sea surface community composed of coastal and oceanic species at sea that might portend significant ecological shifts in the marine environment. |
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An integrated observing system for monitoring marine debris and biodiversity Maximenko, N., and 17 others including A. Shcherbina, "An integrated observing system for monitoring marine debris and biodiversity," Oceanography, 34, 52-59, doi:10.5670/oceanog.2021.supplement.02-22, 2021. |
1 Dec 2021 ![]() |
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High-resolution observations of the North Pacific transition layer from a Lagrangian float Kaminski, A.K., E.A. D'Asaro, A.Y. Shcherbina, and R.R. Harcourt, "High-resolution observations of the North Pacific transition layer from a Lagrangian float," J. Phys. Oceanogr., 51, 3163-3181, doi:10.1175/JPO-D-21-0032.1, 2021. |
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1 Oct 2021 ![]() |
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A crucial region of the ocean surface boundary layer (OSBL) is the strongly-sheared and -stratified transition layer (TL) separating the mixed layer from the upper pycnocline, where a diverse range of waves and instabilities are possible. Previous work suggests that these different waves and instabilities will lead to different OSBL behaviours. Therefore, understanding which physical processes occur is key for modelling the TL. Here we present observations of the TL from a Lagrangian float deployed for 73 days near Ocean Weather Station Papa (50°N, 145°W) during Fall 2018. The float followed the vertical motion of the TL, continuously measuring profiles across it using an ADCP, temperature chain and salinity sensors. The temperature chain made depth/time images of TL structures with a resolution of 6 cm and 3 seconds. These showed the frequent occurrence of very sharp interfaces, dominated by temperature jumps of O(1)°C over 6 cm or less. Temperature inversions were typically small (less than about 10 cm), frequent, and strongly-stratified; very few large overturns were observed. The corresponding velocity profiles varied over larger length scales than the temperature profiles. These structures are consistent with scouring behaviour rather than KelvinHelmholtz-type overturning. Their net effect, estimated via a Thorpe-scale analysis, suggests that these frequent small temperature inversions can account for the observed mixed layer deepening and entrainment flux. Corresponding estimates of dissipation, diffusivity, and heat fluxes also agree with previous TL studies, suggesting that the TL dynamics is dominated by these nearly continuous 10-cm scale mixing structures, rather than by less frequent larger overturns. |
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Frontal convergence and vertical velocity measured by drifters in the Alboran Sea Tarry, D.R., S. Essink, A. Pascual, S. Ruiz, P.-M. Poulain, T. Özgökmen, L.R. Centurioni, J.T. Farrar, A. Shcherbina, A. Mahadevan, and E. D'Asaro, "Frontal convergence and vertical velocity measured by drifters in the Alboran Sea," J. Geophys. Res., 126, doi:10.1029/2020JC016614, 2021. |
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1 Apr 2021 ![]() |
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Vertical transport generated by mesoscale and submesoscale flows plays a key role in the exchange of physical and biogeochemical properties between the surface and the ocean interior. Using multiple simultaneous drifter observations, we compute spatial gradients of velocity to obtain estimates of the divergence field. Thanks to the fact that drifters were deployed at two different depths, we can observe the vertical dependence of divergence in the upper 15 m and estimate the associated vertical velocity. In this study, we estimate divergence and vertical velocity in a ~1-m/s semipermanent frontal jet in the Alboran Sea by making use of a multiplatform data set including 82 drifters, a Lagrangian float, and along-shiptrack profile timeseries of temperature and salinity. |
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Restratification at a California Current upwelling front. Part I: Observations Johnson, L., C.M. Lee, E.A. D'Asaro, L. Thomas, and A. Shcherbina, "Restratification at a California Current upwelling front. Part I: Observations," J. Phys. Oceanogr., 50, 14-55-1472, doi:10.1175/JPO-D-19-0203.1, 2020. |
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6 May 2020 ![]() |
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A coordinated survey between a subsurface Lagrangian float and a ship-towed Triaxus profiler obtained detailed measurements of a restratifying surface intensified front (above 30 m) within the California Current System. The survey began as downfront winds incited mixing in the boundary layer. As winds relaxed and mixing subsided, the system entered a different dynamical regime as the front developed an overturning circulation with large vertical velocities that tilted isopycnals and stratified the upper ocean within a day. The horizontal buoyancy gradient was 1.5 x 10-6 s-2 and associated with vorticity, divergence, and strain that approached the Coriolis frequency. Estimates of vertical velocity from the Lagrangian float reached 1.2 x 10-3 m s-1. These horizontal gradients and vertical velocities were consistent with submesoscale dynamics that are distinct from the classic quasigeostrophic framework used to describe larger-scale flows. Vertical and horizontal gradients of velocity and buoyancy in the vicinity of the float revealed that sheared currents differentially advected the horizontal buoyancy gradient to increase vertical stratification. This was supported by analyses of temperature and salinity gradients that composed the horizontal and vertical stratification. Potential vorticity was conserved during restratification at 16 m, consistent with adiabatic processes. Conversely, potential vorticity near the surface (8 m) increased, highlighting the role of friction in modulating near-surface stratification. The observed increase in stratification due to these submesoscale processes was equivalent to a heat flux of 2000 W m-2, which is an order-of-magnitude larger than the average observed surface heat flux of 100 W m-2. |
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Novel and flexible approach to access the open ocean: Uses of sailing research vessel Lady Amber during SPURS-2 Rainville, L., L.R. Centurioni, W.E. Asher, C.A. Clayson, K. Drushka, J.B. Edson, B.A. Hodges, V. Hormann, J.T. Farai, J.J. Schanze, and A.Y. Shcherbina, "Novel and flexible approach to access the open ocean: Uses of sailing research vessel Lady Amber during SPURS-2," Oceanography, 32, 116-121, doi:10.5670/oceanog.2019.219, 2019. |
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14 Jun 2019 ![]() |
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SPURS-2 (Salinity Processes in the Upper-ocean Regional Study 2) used the schooner Lady Amber, a small sailing research vessel, to deploy, service, maintain, and recover a variety of oceanographic and meteorological instruments in the eastern Pacific Ocean. Low operational costs allowed us to frequently deploy floats and drifters to collect data necessary for resolving the regional circulation of the eastern tropical Pacific. The small charter gave us the opportunity to deploy drifters in locations chosen according to current conditions, to recover and deploy various autonomous instruments in a targeted and adaptive manner, and to collect additional near-surface and atmospheric measurements in the remote SPURS-2 region. |
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Rain and sun create slippery layers in the Eastern Pacific Fresh Pool Shcherbina, A.Y., E.A. D'Asaro, and R.R. Harcourt, "Rain and sun create slippery layers in the Eastern Pacific Fresh Pool," Oceanography, 32, 98-107, doi:10.5670/oceanog.2019.217, 2019. |
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14 Jun 2019 ![]() |
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An autonomous Lagrangian float equipped with a high-resolution acoustic Doppler current profiler observed the evolution of upper-ocean stratification and velocity in the Eastern Pacific Fresh Pool for over 100 days in AugustNovember 2016. Although convective mixing homogenized the water column to 40 m depth almost every night, the combination of diurnal warming on clear days and rainfall on cloudy days routinely produced strong stratification in the upper 10 m. Whether due to thermal or freshwater effects, the initial strong stratification was mixed downward and incorporated in the bulk of the mixed layer within a few hours. Stratification cycling was associated with pronounced variability of ocean surface boundary layer turbulence and vertical shear of wind-driven (Ekman) currents. Decoupled from the bulk of the mixed layer by strong stratification, warm and fresh near-surface waters were rapidly accelerated by wind, producing the well-known "slippery layer" effect, and leading to a strong downwind near-surface distortion of the Ekman profile. A case study illustrates the ability of the new generation of Lagrangian floats to measure rapidly evolving temperature, salinity, and velocity, including turbulent and internal wave components. Quantitative interpretation of the results remains a challenge, which can be addressed with high-resolution numerical modeling, given sufficiently accurate air-sea fluxes. |
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SPURS-2: Salinity Processes in the Upper-Ocean Regional Study 2 The Eastern Equatorial Pacific Experiment Lindstrom, E.J., J.B. Edson, J.J. Schanze, and A.Y. Shcherbina, "SPURS-2: Salinity Processes in the Upper-Ocean Regional Study 2 The Eastern Equatorial Pacific Experiment," Oceanography, 32, 15-19, doi:10.5670/oceanog.2019.207, 2019. |
14 Jun 2019 ![]() |
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Drogue-loss detection for surface drifters during the Lagrangian Submesoscale Experiment (LASER) Haza, A.C., and 12 others, including E.A. D'Asaro and A. Shcherbina, "Drogue-loss detection for surface drifters during the Lagrangian Submesoscale Experiment (LASER)," J. Atmos. Ocean. Technol., 35, 705-725, doi:10.1175/JTECH-D-17-0143.1, 2018. |
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1 Apr 2018 ![]() |
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The Lagrangian Submesoscale Experiment (LASER) was designed to study surface flows during winter conditions in the northern Gulf of Mexico. More than 1000 mostly biodegradable drifters were launched. The drifters consisted of a surface floater extending 5 cm below the surface, containing the satellite tracking system, and a drogue extending 60 cm below the surface, hanging beneath the floater on a flexible tether. On some floats, the drogue separated from the floater during storms. This paper describes methods to detect drogue loss based on two properties that distinguish drogued from undrogued drifters. First, undrogued drifters often flip over, pointing their satellite antenna downward and thus intermittently reducing the frequency of GPS fixes. Second, undrogued drifters respond to wind forcing more than drogued drifters. A multistage analysis is used: first, two properties are used to create a preliminary drifter classification; then, the motion of each unclassified drifter is compared to that of its classified neighbors in an iterative process for nearly all of the drifters. The algorithm classified drifters with a known drogue status with an accuracy of virtually 100%. Drogue loss times were estimated with a precision of less than 0.5 and 3 h for 60% and 85% of the drifters, respectively. An estimated 40% of the drifters lost their drogues in the first 7 weeks, with drogue loss coinciding with storm events, particularly those with steep waves. Once the drogued and undrogued drifters are classified, they can be used to quantify the differences in material dispersion at different depths. |
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Observing finescale oceanic velocity structure with an autonomous Nortek acoustic Doppler current profiler Shcherbina, A.Y., E.A. D'Asaro, and S. Nylund, "Observing finescale oceanic velocity structure with an autonomous Nortek acoustic Doppler current profiler," J. Atmos. Oceanic Technol., 35, 411–427, doi:10.1175/JTECH-D-17-0108.1, 2018. |
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1 Feb 2018 ![]() |
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This paper describes the instrumentation and techniques for long-term targeted observation of the centimeter-scale velocity structure within the oceanic surface boundary layer, made possible by the recent developments in capabilities of autonomous platforms and self-contained pulse-coherent acoustic Doppler current profilers (ADCPs). Particular attention is paid to the algorithms of ambiguity resolution ("unwrapping") of pulse-coherent Doppler velocity measurements. The techniques are demonstrated using the new Nortek Signature1000 ADCP mounted on a Lagrangian float, a combination shown to be capable of observing ocean turbulence in a number of recent studies. Statistical uncertainty of the measured velocities in relation to the ADCP setup is also evaluated. Described techniques and analyses should be broadly applicable to other autonomous and towed applications of pulse-coherent ADCPs. |
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Observations of near-surface current shear help describe oceanic oil and plastic transport Laxague, N.J.M., and 10 others, including A. Shcherbina, "Observations of near-surface current shear help describe oceanic oil and plastic transport," Geophys. Res. Lett., 45 ,245-249, doi:10.1002/2017GL075891, 2018. |
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16 Jan 2018 ![]() |
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Plastics and spilled oil pose a critical threat to marine life and human health. As a result of wind forcing and wave motions, theoretical and laboratory studies predict very strong velocity variation with depth over the upper few centimeters of the water column, an observational blind spot in the real ocean. Here we present the first-ever ocean measurements of the current vector profile defined to within 1 cm of the free surface. In our illustrative example, the current magnitude averaged over the upper 1 cm of the ocean is shown to be nearly four times the average over the upper 10 m, even for mild forcing. Our findings indicate that this shear will rapidly separate pieces of marine debris which vary in size or buoyancy, making consideration of these dynamics essential to an improved understanding of the pathways along which marine plastics and oil are transported. |
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Ocean convergence and the dispersion of flotsam D'Asaro, E.A., A.Y. Shcherbina, and 17 others, "Ocean convergence and the dispersion of flotsam," Proc. Nat. Acad. Sci. U.S.A., 115, 1162-1167, doi:10.1073/pnas.1718453115, 2018. |
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16 Jan 2018 ![]() |
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Ocean currents move material released on the ocean surface away from the release point and, over time, spread it over an increasingly large area. However, observations also show high concentrations of the material even after significant spreading. This work examines a mechanism for creating such concentrations: downwelling of water at the boundaries of different water masses concentrates floating material at this boundary. Hundreds of satellite-tracked drifters were released near the site of the 2010 Deepwater Horizon oil spill. Surprisingly, most of these gathered into a single cluster less than 100 m in size, dramatically demonstrating the strength of this mechanism. |
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Autonomous multi-platform observations during the Salinity Processes in the Upper-ocean Regional Study Lindstrom, E.J., A.Y. Shcherbina, L. Rainville, J.T. Farrar, L.R. Centurioni, S. Dong, E.A. D’Asaro, C. Eriksen, D.M. Fratantoni, B.A. Hodges, V. Hormann, W.S. Kessler, C.M. Lee, S.C. Riser, L. St. Laurent, and D.L. Volkov, "Autonomous multi-platform observations during the Salinity Processes in the Upper-ocean Regional Study," Oceanography, 38-48, doi:, 2017. |
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1 Jun 2017 ![]() |
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The Salinity Processes in the Upper-ocean Regional Study (SPURS) aims to understand the patterns and variability of sea surface salinity. In order to capture the wide range of spatial and temporal scales associated with processes controlling salinity in the upper ocean, research vessels delivered autonomous instruments to remote sites, one in the North Atlantic and one in the Eastern Pacific. Instruments sampled for one complete annual cycle at each of these two sites, which are subject to contrasting atmospheric forcing. The SPURS field programs coordinated sampling from many different platforms, using a mix of Lagrangian and Eulerian approaches. This article discusses the motivations, implementation, and first results of the SPURS-1 and SPURS-2 programs. |
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Northern Arabian Sea Circulation-Autonomous Research (NASCar): A research initiative based on autonomous sensors Centurioni, L.R., and 33 others, including R.R. Harcourt, C.M. Lee, L. Rainville, and A.Y. Shcherbina, "Northern Arabian Sea Circulation-Autonomous Research (NASCar): A research initiative based on autonomous sensors," Oceanography, 30, 74-87, doi:10.5670/oceanog.2017.224, 2017. |
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1 Jun 2017 ![]() |
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The Arabian Sea circulation is forced by strong monsoonal winds and is characterized by vigorous seasonally reversing currents, extreme differences in sea surface salinity, localized substantial upwelling, and widespread submesoscale thermohaline structures. Its complicated sea surface temperature patterns are important for the onset and evolution of the Asian monsoon. This article describes a program that aims to elucidate the role of upper-ocean processes and atmospheric feedbacks in setting the sea surface temperature properties of the region. The wide range of spatial and temporal scales and the difficulty of accessing much of the region with ships due to piracy motivated a novel approach based on state-of-the-art autonomous ocean sensors and platforms. The extensive data set that is being collected, combined with numerical models and remote sensing data, confirms the role of planetary waves in the reversal of the Somali Current system. These data also document the fast response of the upper equatorial ocean to monsoon winds through changes in temperature and salinity and the connectivity of the surface currents across the northern Indian Ocean. New observations of thermohaline interleaving structures and mixing in setting the surface temperature properties of the northern Arabian Sea are also discussed. |
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Optimal planning and sampling predictions for autonomous Lagrangian platforms and sensors in the northern Arabian Sea Lermusiaux, P.F.J., and 12 others, including A.Y. Shcherbina and C.M. Lee, "Optimal planning and sampling predictions for autonomous Lagrangian platforms and sensors in the northern Arabian Sea," Oceanography, 30, 172-185, doi:10.5670/oceanog.2017.242, 2017. |
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1 Jun 2017 ![]() |
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Where, when, and what to sample, and how to optimally reach the sampling locations, are critical questions to be answered by autonomous and Lagrangian platforms and sensors. For a reproducible scientific sampling approach, answers should be quantitative and provided using fundamental principles. This article reviews concepts and recent progress toward this principled approach, focusing on reachability, path planning, and adaptive sampling, and presents results of a real-time forecasting and planning experiment completed during FebruaryApril 2017 for the Northern Arabian Sea Circulation-autonomous research program. The predictive skill, layered fields, and uncertainty estimates obtained using the MIT MSEAS multi-resolution ensemble ocean modeling system are first studied. With such inputs, deterministic and probabilistic three-dimensional reachability forecasts issued daily for gliders and floats are then showcased and validated. Finally, a Bayesian adaptive sampling framework is shown to forecast in real time the observations that are most informative for estimating classic ocean fields and also secondary variables such as Lagrangian coherent structures. |
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Model-aided Lagrangian interpretation of non-synoptic estuarine observations Shcherbina, A.Y., C.L. McNeil, and A.M. Baptista, "Model-aided Lagrangian interpretation of non-synoptic estuarine observations," Limnol. Oceanogr. Method., 14, 397-407, doi:10.1002/lom3.10098, 2016. |
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1 Jun 2016 ![]() |
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We propose a novel method for constructing a pseudo-synoptic view of estuarine features from non-synoptic observations captured by mobile platforms. The model-aided Lagrangian interpretation (MALI) method is based on relocating observations to a common reference moment in time along three-dimensional Lagrangian trajectories derived from a numerical model of estuarine circulation. The method relies on the model skill to capture large-scale circulation features, and on high-resolution in situ observations to characterize small-scale hydrographic structure. We demonstrate our technique by applying MALI to autonomous underwater vehicle observations in the Columbia River estuary, with the aid of a validated unstructured-grid finite-element numerical simulation. The method can be readily adapted to a broader range of environments, observational platforms, and model-data combinations. |
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Submesoscale streamers exchange water on the north wall of the Gulf Stream Klymak, J.M., R.K. Shearman, J. Gula, C.M. Lee, E.A. D'Asaro, L.N. Thomas, R.R. Harcourt, A.Y. Shcherbina, M.A. Sundermeyer, J. Molemaker, and J.C. McWilliams, "Submesoscale streamers exchange water on the north wall of the Gulf Stream," Geophys. Res. Lett., 43, 1226-1233, doi:10.1002/2015GL067152, 2016. |
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The Gulf Stream is a major conduit of warm surface water from the tropics to the subpolar North Atlantic. Here we observe and simulate a submesoscale (<20 km) mechanism by which the Gulf Stream exchanges water with subpolar water to the north. Along isopycnals, the front has a sharp compensated temperature-salinity contrast, with distinct mixed water between the two water masses 2 and 4 km wide. This mixed water does not increase downstream despite substantial energy available for mixing. A series of streamers detrain this water at the crest of meanders. Subpolar water replaces the mixed water and resharpens the front. The water mass exchange accounts for a northward flux of salt of 0.52.5 psu m2 s-1, (large-scale diffusivity O (100 m2 s-1)). This is similar to bulk-scale flux estimates of 1.2 psu m2 s-1 and supplies fresher water to the Gulf Stream required for the production of 18° subtropical mode water. |
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Symmetric instability, inertial oscillations, and turbulence at the Gulf Stream front Thomas, L.N., J.R. Taylor, E.A. D'Asaro, C.M. Lee, J.M. Klymak, and A. Shcherbina, "Symmetric instability, inertial oscillations, and turbulence at the Gulf Stream front," J. Phys. Oceanogr., 46, 197-217, doi:10.1175/JPO-D-15-0008.1, 2016. |
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The passage of a winter storm over the Gulf Stream observed with a Lagrangian float and hydrographic and velocity surveys provided a unique opportunity to study how the interaction of inertial oscillations, the front, and symmetric instability (SI) shapes the stratification, shear, and turbulence in the upper ocean under unsteady forcing. During the storm, the rapid rise and rotation of the winds excited inertial motions. Acting on the front, these sheared motions modulate the stratification in the surface boundary layer. At the same time, cooling and downfront winds generated a symmetrically unstable flow. The observed turbulent kinetic energy dissipation exceeded what could be attributed to atmospheric forcing, implying SI drew energy from the front. The peak excess dissipation, which occurred just prior to a minimum in stratification, surpassed that predicted for steady SI turbulence, suggesting the importance of unsteady dynamics. The measurements are interpreted using a large-eddy simulation (LES) and a stability analysis configured with parameters taken from the observations. The stability analysis illustrates how SI more efficiently extracts energy from a front via shear production during periods when inertial motions reduce stratification. Diagnostics of the energetics of SI from the LES highlight the temporal variability in shear production but also demonstrate that the time-averaged energy balance is consistent with a theoretical scaling that has previously been tested only for steady forcing. As the storm passed and the winds and cooling subsided, the boundary layer restratified and the thermal wind balance was reestablished in a manner reminiscent of geostrophic adjustment. |
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The LatMix summer campaign: Submesoscale stirring in the upper ocean Shcherbina, A.Y., and 37 others including E. D'Asaro, R.R. Harcourt, C.M. Lee, R.-C. Lien, and T.B. Sanford, "The LatMix summer campaign: Submesoscale stirring in the upper ocean," Bull. Am. Meteor. Soc., 96, 1257-1279, doi:10.1175/BAMS-D-14-00015.1, 2015. |
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1 Aug 2015 ![]() |
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Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.110 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s-1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level. |
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Variability and interleaving of upper-ocean water masses surrounding the North Atlantic salinity maximum Shcherbina, A.Y., E.A. D'Asaro, S.C. Riser, and W.S. Kessler, "Variability and interleaving of upper-ocean water masses surrounding the North Atlantic salinity maximum," Oceanography, 28, 106-113, doi:10.5670/oceanog.2015.12, 2015. |
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The North Atlantic subtropical salinity maximum harbors the saltiest surface waters of the open world ocean. Subduction of these waters gives rise to Subtropical Underwater, spreading the high-salinity signature over the entire basin. The Salinity Processes in the Upper-ocean Regional Study (SPURS) is aimed at understanding the physics controlling the thermohaline structure in the salinity maximum region. A combination of moored and autonomous float observations is used here to describe the vertical water mass interleaving in the area. Seasonal intensification of interleaving in late spring and the abundance of small-scale thermohaline intrusions point to an important role for submesoscale processes in the initial subduction and subsequent evolution of Subtropical Underwater. |
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Variability in near-surface salinity from hours to decades in the eastern North Atlantic: The SPURS region Riser, S.C., J. Anderson, A. Shcherbina, and E.D'Asaro, "Variability in near-surface salinity from hours to decades in the eastern North Atlantic: The SPURS region," Oceanography, 28, 66-77, doi:10.5670/oceanog.2015.11, 2015. |
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We examine the variability of near-surface salinity in a 10° x 10° region of the eastern North Atlantic, the location of the first part of the Salinity Processes in the Upper-ocean Regional Study (SPURS-1). The data used were collected over a two-year period, largely by a group of two types of profiling floats equipped with sensors that record high-resolution temperature and salinity measurements in the upper few meters of the water column. By comparing the SPURS-1 measurements to observations in the area from previous decades, we examine variability at time scales ranging from a few hours (mostly consisting of rainfall-driven decreases in salinity) to diurnal cycles in temperature and salinity, seasonal variability and the annual cycle, and finally to decadal-scale changes. The relationship of near-surface salinity to the hydrological cycle suggests a continuous spectrum of variability in this cycle from hours to decades. |
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Quantifying upper ocean turbulence driven by surface waves D'Asaro, E.A., J. Thomson, A.Y. Shcherbina, R.R. Harcourt, M.F. Cronin, M.A. Hemer, and B. Fox-Kemper, "Quantifying upper ocean turbulence driven by surface waves," Geophys. Res. Lett, 41, 102-107, doi:10.1002/1013GL058193, 2014. |
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1 Jan 2014 ![]() |
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Nearly all operational ocean models use air-sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates. This approach implicitly parameterizes surface wave effects in terms of these inputs. Here, we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves. Under the same wind stress and adjusting for buoyancy flux, we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake. The increase is consistent with models of Langmuir turbulence, in which the wave Stokes drift, and not wave breaking, is the dominant mechanism by which waves energize turbulence in the mixed layer. Applying these same theories globally, we find enhanced mixing and deeper mixed layers resulting from the inclusion of Langmuir turbulence in the boundary layer parameterization, especially in the Southern Ocean. |
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Waves and the equilibrium range at Ocean Weather Station P Thomson, J., E.A. D'Asaro, M.F. Cronin, W.E. Rogers, R.R. Harcourt, and A. Shcherbina, "Waves and the equilibrium range at Ocean Weather Station P," J. Geophys. Res., 118, 5951-5962, doi:10.1002/2013JC008837, 2013. |
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1 Nov 2013 ![]() |
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Wave and wind measurements at Ocean Weather Station P (OWS-P, 50°N 145°W) are used to evaluate the equilibrium range of surface wave energy spectra. Observations are consistent with a local balance between wind input and breaking dissipation, as described by Philips (1985). The measurements include direct covariance wind stress estimates and wave breaking dissipation rate estimates during a 3 week research cruise to OWS-P. The analysis is extended to a wider range of conditions using observations of wave energy spectra and wind speed during a 2 year mooring deployment at OWS-P. At moderate wind speeds (515 m/s), mooring wave spectra are in agreement, within 5% uncertainty, with the forcing implied by standard drag laws and mooring wind measurements. At high wind speeds (>15 m/s), mooring wave spectra are biased low, by 13%, relative to the forcing implied by standard drag laws and mooring wind measurements. Deviations from equilibrium are associated with directionality and variations at the swell frequencies. A spectral wave hindcast accurately reproduces the mooring observations, and is used to examine the wind input. |
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Statistics of vertical vorticity, divergence, and strain in a developed submesoscale turbulence field Shcherbina, A.Y., E.A. D'Asaro, C.M. Lee, J.M. Klymak, M.J. Molemaker, and J.C. McWilliams, "Statistics of vertical vorticity, divergence, and strain in a developed submesoscale turbulence field," Geophys. Res. Lett., 40, 4706-4711, doi:10.1002/grl.50919, 2013. |
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16 Sep 2013 ![]() |
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A detailed view of upper ocean vorticity, divergence, and strain statistics was obtained by a two-vessel survey in the North Atlantic Mode Water region in winter 2012. Synchronous Acoustic Doppler Current Profiler sampling provided the first in situ estimates of the full velocity gradient tensor at O(1 km) scale without the usual mix of spatial and temporal aliasing. The observed vorticity distribution in the mixed layer was markedly asymmetric (skewness 2.5), with sparse strands of strong cyclonic vorticity embedded in a weak, predominantly anticyclonic background. Skewness of the vorticity distribution decreased linearly with depth, disappearing completely in the pycnocline. Statistics of divergence and strain rate generally followed the normal and χ distributions, respectively. These observations confirm a high-resolution numerical model prediction for the structure of the active submesoscale turbulence field in this area. |
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Observations of near-inertial internal gravity waves radiating from a frontal jet Alford, M.H., A.Y. Shcherbina, and M.C. Gregg, "Observations of near-inertial internal gravity waves radiating from a frontal jet," J. Phys. Oceanogr., 43, 1225-1239, doi:10.1175/JPO-D-12-0146.1, 2013. |
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Shipboard ADCP and towed CTD measurements are presented of a near-inertial internal gravity wave radiating away from a zonal jet associated with the Subtropical Front in the North Pacific. Three-dimensional spatial surveys indicate persistent alternating shear layers sloping downward and equatorward from the front. As a result, depth-integrated ageostrophic shear increases sharply equatorward of the front. The layers have a vertical wavelength of about 250 m and a slope consistent with a wave of frequency 1.01 f. They extend at least 100 km south of the front. Time series confirm that the shear is associated with a downward-propagating near-inertial wave with frequency within 20% of f. A slab mixed layer model forced with shipboard and NCEP reanalysis winds suggests that wind forcing was too weak to generate the wave. Likewise, trapping of the near-inertial motions at the low-vorticity edge of the front can be ruled out because of the extension of the features well south of it. Instead, the authors suggest that the wave arises from an adjustment process of the frontal flow, which has a Rossby number about 0.20.3. |
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Offshore transport of shelf waters through interaction of vortices with a shelfbreak current Cenedese, C., R.E. Todd, G.G. Gawarkiewicz, W. Brechner Owens, and A.Y. Shcherbina, "Offshore transport of shelf waters through interaction of vortices with a shelfbreak current," J. Phys. Oceanogr., 45, 905-919, doi:10.1175/JPO-D-12-0150.1, 2013. |
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1 May 2013 ![]() |
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Interactions between vortices and a shelfbreak current are investigated, with particular attention to the exchange of waters between the continental shelf and slope. The nonlinear, three-dimensional interaction between an anticyclonic vortex and the shelfbreak current is studied in the laboratory while varying the ratio ε of the maximum azimuthal velocity in the vortex to the maximum alongshelf velocity in the shelfbreak current. Strong interactions between the shelfbreak current and the vortex are observed when ε > 1; weak interactions are found when ε < 1. When the anticyclonic vortex comes in contact with the shelfbreak front during a strong interaction, a streamer of shelf water is drawn offshore and wraps anticyclonically around the vortex. Measurements of the offshore transport and identification of the particle trajectories in the shelfbreak current drawn offshore from the vortex allow quantification of the fraction of the shelfbreak current that is deflected onto the slope; this fraction increases for increasing values of ε. Experimental results in the laboratory are strikingly similar to results obtained from observations in the Middle Atlantic Bight (MAB); after proper scaling, measurements of offshore transport and offshore displacement of shelf water for vortices in the MAB that span a range of values of ε agree well with laboratory predictions. |
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Chlorophyll bloom development and the subtropical front in the North Pacific Wilson, C., T.A. Villareal, M.A. Brzezinski, J.W. Krause, and A.Y. Shcherbina, "Chlorophyll bloom development and the subtropical front in the North Pacific," J. Geophys. Res., 118, 1473-1488, doi:10.1002/jgrc.20143, 2013. |
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1 Mar 2013 ![]() |
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In late summer, satellite ocean color data consistently show localized chlorophyll blooms in the oligotrophic NE Pacific. Based on historical data and the results from recent cruises, these blooms are associated with elevated diatom abundance. However, the physical dynamics that stimulate the blooms remain unknown. Mechanisms suggested to be driving the blooms include mixing at the subtropical front, breaking of internal waves at the critical latitude, shoaling of the mixed layer depth, eddy interactions, and winter mixing of nutrients. To examine these hypotheses, we use data from four summer cruises (2002, 2007, 2008, and 2009) in this region that sampled near a bloom temporally and/or spatially. Conditions associated with five blooms (two blooms were sampled in 2009) are examined. Each area was sampled at a different stage in bloom development, including prebloom, initiation, full bloom, decline, and postbloom conditions. No one variable is found which can explain unequivocally the development of a chlorophyll bloom at a certain location. We describe a set of conditions that could result in the injection of nutrients into the surface water to stimulate a bloom. This "perfect storm" of conditions requires a subsurface stratification minimum layer that intersects the nutricline and that this minimum is close to the base of the mixed layer. These conditions are not predictable in the sense of an annual climatology; however, they do occur often enough to create a reasonably certain, if spatially variable, summer NE Pacific bloom. |
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Three-dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the North Pacific subtropical frontal zone Shcherbina, A.Y., M.C. Gregg, M.H. Alford, M.H., and R.R. Harcourt, "Three-dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the North Pacific subtropical frontal zone," J. Phys. Oceanogr., 40, 1669-1689, doi:10.1175/2010JPO4373.1, 2010. |
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1 Aug 2010 ![]() |
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Four instances of persistent intrusive deformation of the North Pacific Subtropical Front were tagged individually by a Lagrangian float and tracked for several days. Each feature was mapped in three dimensions using repeat towed observations referenced to the float. Isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front. All deformations appeared as protrusions of relatively cold, and fresh, water across the front. No corresponding features of the opposite sign or isolated lenslike structures were observed. The sheets were O(10 m) thick, protruded about 10 km into the warm saline side of the front, and were coherent for 1030 km along the front. Having about the same thickness and cross-frontal extent as the sheets, tongues extended less than 5 km along the front. |
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Characterizing thermohaline intrusions in the North Pacific subtropical frontal zone Shcherbina, A.Y., M.C. Gregg, M.H. Alford, and R.R. Harcourt, "Characterizing thermohaline intrusions in the North Pacific subtropical frontal zone," J. Phys. Oceanogr., 39, 2735-2756, 2009. |
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A monthlong field survey in July 2007, focused on the North Pacific subtropical frontal zone (STFZ) near 30°N, 158°W, combined towed depth-cycling conductivity-temperature-depth (CTD) profiling with shipboard current observations. Measurements were used to investigate the distribution and structure of thermohaline intrusions. The study revealed that local extrema of vertical salinity profiles, often used as intrusion indicators, were only a subset of a wider class of distortions in thermohaline fields due to interleaving processes. A new method to investigate interleaving based on diapycnal spiciness curvature was used to describe an expanded class of laterally coherent intrusions. STFZ intrusions were characterized by their overall statistics and by a number of case studies. Thermohaline interleaving was particularly intense within 5 km of two partially compensated fronts, where intrusions with both positive and negative salinity anomalies were widespread. The vertical and cross-frontal scales of the intrusions were on the order of 10 m and 5 km, respectively. Though highly variable, the slopes of these features were typically intermediate between those of isopycnals and isohalines. Although the influence of double-diffusive processes sometime during the evolution of intrusions could not be excluded, the broad spectrum of the observed features suggests that any role of double diffusion was secondary. |
In The News
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Untangling the ocean trash glut, one 'ghost net' at a time Christian Science Monitor, Doug Struck APL-UW oceanographer Andrey Shcherbina, who studies ocean circulation patterns, hitched a ride on a ship of opportunity to deploy sensors in the Pacific garbage patch. |
19 Jun 2020
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Temporary 'bathtub drains' in the ocean concentrate flotsam UW News, Hannah Hickey An experiment featuring the largest flotilla of sensors ever deployed in a single area provides new insights into how marine debris, or flotsam, moves on the surface of the ocean. |
18 Jan 2018
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