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OS4.1

This open session welcomes presentations in all aspects of ocean processes and oceanographic techniques that are not covered in specialised sessions, as well as advances due to new instruments and techniques such as gliders and AUVs. This includes all marine disciplines as well as interaction with the atmosphere and the cryosphere. Global studies and topics that have global relevance are welcome (i.e. both open ocean and shelf seas). Studies focusing on ocean processes might include turbulent mixing, phytoplankton bloom initiation, or air-sea interactions, for example. Studies about the development of new oceanographic techniques might include robotics, design of numerical models or parameterisations, applications of novel instrumentation, or novel applications of traditional technology.

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Convener: Callum RolloECSECS | Co-conveners: Isabelle GiddyECSECS, Matjaz Licer, Charles Troupin
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| Tue, 05 May, 10:45–12:30 (CEST)

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Chat time: Tuesday, 5 May 2020, 10:45–12:30

Chairperson: Callum Rollo
D2800 |
EGU2020-183
| Highlight
Tobias Ehmen, Katy Sheen, Andrew Watson, Alexander Brearley, Matthew Palmer, and Daniel Roper

Sub-mesoscale variability in the ocean is poorly understood. The challenge is to observe oceanic thermohaline structures on sufficiently fine space and time scales. One promising approach is seismic oceanography, which applies acoustic reflection techniques to image temperature and salinity gradients within the water column. Here, we present three acoustic oceanographic datasets showing different survey methods and assess their advantages and disadvantages.

Firstly, seismic images from a 2D seismic survey in the Sub-Antarctic southwest Atlantic Ocean are shown. The study site is located northeast of Drake Passage, through which Pacific and Antarctic waters flow to merge with those from the Atlantic, making it a key confluence region. The data show detailed images of sub-mesoscale structures in the upper ocean. Future work will make use of coincident XBT measurements to invert the acoustic data and create detailed 2D maps of temperature distribution.

The second dataset contains samples from a 3D seismic survey in the narrowest part of the Mozambique Channel, which is affected by eddies and changes in transport direction and volume. It acts as a pacemaker for the Agulhas Current system, which plays an important role in global heat transport. The dataset, courtesy of Schlumberger Ltd, combines a high signal to noise ratio with a dense data grid, where locations are sampled several times over several days. These data were used to create time lapse images of the area, providing an invaluable insight into the variabilities in the Mozambique Channel.

Despite a lot of advantages, seismic surveys are generally expensive and lack mobility and versatility. Therefore, another acoustic dataset using a hull-mounted EK80 scientific echo sounder, as part of the ICEBERGS project, is presented as a cheaper and more readily available alternative. Images from the West Antarctic Peninsula show thermohaline structures recorded along the actively de-glaciating margin, contributing to the understanding of underlying physical processes that modulate the flux of oceanic heat to the Antarctic cryosphere, and how and where glacial meltwater is discharged, transported and modified. Furthermore, recording and processing difficulties are discussed.

Lastly, acoustic forward modelling work is discussed, which will wrap up the analysis of the methods presented earlier. Based on the three datasets, the use of different acoustic sources will be forward modelled. Through this ideal sources of different sizes and configurations for seismic oceanography can be analysed. Is it feasible to use acoustic sources small enough to be attached to autonomous vehicles, in order to overcome the current difficulties in extracting temporal variability of oceanic fine structure?

D2801 |
EGU2020-10499
| Highlight
Karen J. Heywood, Elizabeth Siddle, Callum Rollo, Ben Webber, Rob Hall, Gillian Damerell, Philip Leadbitter, Gareth Lee, Peter Bromley, Paul Stafford, Alastair Nichol, and Hugh Maclean

This PICO presentation describes a recent demonstration mission of our wave-propelled autonomous vehicle, an AutoNaut named Caravela. Caravela has been designed and built to carry and deploy a profiling ocean glider at a specified location and time. This has applications for example in transporting an ocean glider to a remote location without use of a research vessel, or initiating a glider campaign at a particular time such as prior to a hurricane or the spring bloom.

 

In January-February 2020 we participated in the international Eurec4a field campaign in the tropical Atlantic to the east of Barbados. Caravela was deployed from Barbados and carried a Seaglider to release at the study site. The observational campaign was designed to occupy a time series site with three Seagliders (making intensive measurements of upper ocean properties) and the AutoNaut (making continuous measurements of surface meteorology, radiation and surface ocean currents).  Here we describe the technological challenges, the field campaign and the preliminary results of the scientific observations from Caravela and the Seagliders. The aim is to use the observations to calculate the air-sea fluxes and ultimately to close a mixed layer heat budget for the observation site.

D2802 |
EGU2020-7026
Zoé Koenig, Ilker Fer, Eivind Kolås, Trygve Fossum, Petter Norgren, and Martin Ludvigsen

Measurements made at an Arctic thermohaline front show turbulence production through convection and forced symmetric instability, a mechanism drawing energy from the frontal geostrophic current. Destabilizing surface buoyancy fluxes from a combination of heat loss to the atmosphere and cross-front Ekman transport by down-front winds reduce the potential vorticity in the upper ocean. The front, located in the Nansen Basin close to the sea ice edge, separates the cold and fresh surface melt water from the warm and saline mixed layer. High resolution temperature, salinity, current and turbulence data were collected in the upper 100 m, on 18 September 2018 across the front from a research vessel and an autonomous underwater vehicle. The AUV was deployed to autonomously collect high resolution data across the front using adaptive sampling. Both front detection and sampling location were decided by a state-based autonomous agent running onboard the AUV, optimizing data collection across and along the front.

In addition to convection by heat loss to atmosphere and mechanical forcing by moderate wind in the mixed layer, forced symmetric instability contributed with comparable magnitude in generation of turbulence at the front location down to 40 m depth. This turbulence was associated with turbulent heat fluxes of up to 10 W.m-2, eroding the warm and cold intrusions observed at respectively 35 and 55 m depth. A similar frontal structure has been crossed by a Seaglider in the same region 10 days after our survey. The submesoscale-to-turbulence scale transitions and resulting mixing can be widespread and important in the Atlantic sector of the Arctic Ocean.

D2803 |
EGU2020-1119
Bastien Queste

The physical dynamics of the Sea of Oman are well resolved on meso- and basin-scales. The most prominent features are the slope current of the Persian Gulf Water (PGW), an energetic field of persistent eddies and circulation driven by seasonal monsoon wind regimes. Past work has shown that both oxygenation of the deep oxygen minimum zone and stimulation of local surface primary production are driven by submesoscale processes. In contrast to the pronounced summer-monsoon upwelling in the Arabian Sea, upwelling at the northern Omani shelf appears in the form of short irregular events. The main drivers for local upwelling and the exchange of water and its properties across the shelf break are not fully resolved. In particular, the relative importance of the two dominant causes of upwelling (ekman dynamics and eddy/topography interactions) and their interactions with the PGW slope-current are not known. Cross-shelf coupling is strongly determined by processes on the sub-mesoscale with weak surface signatures preventing analysis through remote sensing. The high system complexity and the lack of adequate observations explain past difficulties in resolving cross-shelf transport and local upwelling responsible for increased primary productivity and OMZ oxygenation.

Here we present new results identifying the submesoscale processes which control productivity and oxygenation in the region at a scale not previously described. These observations build on past work and illustrate how autonomous underwater vehicles can bring forward a full system understanding from basin-wide circulation and description of large ocean currents to submesoscale processes responsible for controlling biogeochemical cycling from a single campaign using standard ocean sensors and utilising the vehicles' inherent ability to measure upwelling and currents. We hope to illustrate the multidisciplinarity and flexibility of autonomous platforms in situations where vessels may not easily survey.

D2804 |
EGU2020-1591
Sultan Albarakati, Ricardo Lima, thomas Theussl, Ibrahim Hoteit, and Omar Knio

We develop a new approach for solving optimal time and energy-trajectory planning problems for Autonomous Underwater Vehicles (AUVs) in transient, 3D ocean currents. Realistic forecasts using an Ocean General Circulation Model (OGCM) are used for this purpose. The approach is based on decomposing the problem into a minimal time problem, followed by minimal energy subproblems. In both cases, a Non-Linear Programming (NLP) formulation is adopted. The methodology is first tested in idealized, steady, 2D settings, to verify the effectiveness of the method in addressing the multi-objective optimization problem. The scheme is then demonstrated for time-energy trajectory planning problems in the Gulf of Aden. In particular, the numerical experiments illustrate the capability of generating Pareto optimal solutions in a broad range of mission durations. In addition, the analysis also highlights how the methodology effectively exploits both the vertical structure of the current field, as well as its unsteadiness, namely, to minimize travel time and energy consumption.

D2805 |
EGU2020-3086
Gillian Damerell, Rob Hall, and Peter Sheehan

In recent years the UEA glider group worked with Kongsberg Maritime and Rockland Scientific Inc. (RSI) to develop and test an integrated microstructure system which could be mounted on Seagliders.   Existing RSI microstructure packages such as the MicroRider could not be used on Seagliders because of a geometry mismatch with the shape of the Seaglider’s hull that made mounting difficult, and because the size of those packages added an unacceptable drag.  We also required a more sophisticated software interface so that the RSI system could be controlled by the standard Seaglider scientific logger payload control software.

 

Since the initial sea trials in 2015, microstructure Seagliders have been deployed on missions in the Bay of Bengal, the Faroe Shetland Channel, east of the Bahamas, and the Weddell Sea.  Early successes were followed by a number of technical problems which have now been resolved.  Improvements in the glider flight model have led to improvements in microstructure estimates.  The most recent deployment in the Weddell Sea allowed comparison between Seaglider estimates of dissipation and those from an established microstructure profiler (MSS90).  Dissipation estimates measured by the Seaglider system varied between 10-10 and 10-5 W kg-1, with higher values generally closer to the surface.  Those observed by the MSS were similar at depth but slightly higher in the top 200 m.  Further work will aim to understand these differences.

D2806 |
EGU2020-3546
Alisa Yakhontova, Roelof Rietbroek, Jens Schröter, Nadja Jonas, Christina Lück, and Bernd Uebbing

Improved estimates of temperature, salinity, and sea surface height changes are computed from radar altimetry, satellite gravimetry and Argo profiles, and validated by the in situ ocean bottom pressure measurements in a South Atlantic transect of the Antarctic Circumpolar current. Using satellite gravimetry and altimetry observations, separate contributions to the global sea level can be estimated, but a regional solution is more challenging. Furthermore, Argo derived steric sea level change suffers from spatio-temporal sampling problems, and some signals are not well captured, e.g. in the deeper ocean below 2000m, around the boundary currents, in the Arctic or in the shelf/coastal regions. Jointly processing radar altimetry, Argo and data from the Gravity Recovery and Climate Experiment (GRACE), would allow to correct the deficiencies of the individual datasets, and produce observation based estimates of consistent temperature, salinity and sea surface height changes. In order to pave the way for an advanced joint inversion scheme that additionally resolves for temperature and salinity, the observation equations are formulated which link the satellite observations to temperature and salinity at depth. Observations in the South Atlantic region are compared with simulations from the FESOM model in terms of variability and the model data is used to find the spatial coherence of the signals at the sites with the surrounding ocean. The experiment is performed in the Southern Atlantic Ocean, where the estimates can be validated using an array of in situ ocean bottom pressure observations.

D2807 |
EGU2020-22115
| Highlight
Pierre-Amaël Auger, Valerie Villegas, Ali Belmadani, David Donoso, Tomas Berger, and Samuel Hormazabal

In recent years, quasi-zonal mesoscale jet-like features, also called “striations”, have been ubiquitously detected in the time-mean circulation of the world ocean using satellite altimetry and in situ data. These alternating bands of eastward/westward flow are able to advect and mix physical properties. Yet, their impact on biogeochemistry, and potentially marine ecosystems, has not been assessed yet.

In eastern boundary upwelling systems, a mesoscale structuration of biogeochemical properties may be associated to striations through the interaction of zonal flows with sharp coastal-offshore background gradients (stirring). Transport patterns by mesoscale eddies (trapping) may also be involved as striations were noticeably suggested to result from the organization of the mesoscale eddy field as preferred eddy tracks in the eastern South Pacific upwelling system (off central Chile).

In this region, we evaluate the expression of striations in satellite records of ocean color and in a set of numerically simulated biogeochemical tracers (chlorophyll, carbon, primary production, oxygen, nutrients). A multi-decadal hindcast simulation of the physical-biogeochemical dynamics was run over the period 1984-2013 using the ROMS-PISCES (for Regional Oceanic Modeling System - Pelagic Interactions Scheme for Carbon and Ecosystem Studies) platform at an eddy-resolving resolution. High-pass spatial filtering is used to remove the large-scale signal in time-averaged satellite data and model outputs, and subsequently evaluate the match between striations and biogeochemical tracer anomalies in the model and observations. The relation between striations and the shape of the coastal-offshore gradient of the phytoplankton biomass and the oxygen-minimum zone is then deduced in the CTZ, and further in the open ocean region. The fraction of tracer anomalies associated to striations is quantified, and the respective potential role of stirring and eddy trapping is explored by matching quasi-zonal bands of sea level anomaly, geostrophic currents and biogeochemical tracers on moving frames of variable widths from 3 months to several years. The role played by eddy trapping is then confirmed by a composite analysis based upon automated eddy tracking.

D2808 |
EGU2020-19128
Katja Schmidt, Sophie Anna Luise Paul, and Cornelia Kriete

Sampling and analysis of trace elements in open seawater and in sediment pore water in the deep sea is challenging due to small sample volumes and matrix effects. Here we evaluate an alternative method using the technique of diffusive gradients in thin films (DGT passive samplers), focussing on rare earth elements and yttrium (REY). DGT measures the labile fraction of metals in situ by fixing them on a Chelex resin after diffusion through a gel layer, providing a diffusive flux and averaged in situ concentrations of elements during the time of deployment. As the accumulated element concentrations increase with exposure time to solution, long-term deployment times overcome low trace metal concentrations in seawater and pore water. So far, no deep-sea applications of passive samplers are yet reported.

Sampling was performed in bottom seawater and surface sediments in the German licence area for manganese nodule exploration in the Clarion Clipperton Zone (CCZ, research cruise SO268 in April/May 2019), deployment times ranged from 12 hours in sediments to 4 weeks in open seawater.

Seawater DGT’s were deployed 0.5 m to 8 m above the seafloor. PAAS-normalized REY show the typical seawater pattern, with increase from LREE to HREE, a strong negative Ce anomaly, a kink from Gd to Tb, and a pronounced positive Y/Ho anomaly. The pattern and calculated concentrations agree very well with reported dissolved REY (<0.2 µm) for Pacific deep water (Alibo and Nozaki, 1999). Sediment DGT sticks were deployed in cores taken with a multicorer and cover the first 15 cm of the sediment. They provide in situ high-resolution profiles of trace metal fluxes and were analysed in 0.5 cm to 2 cm segments. We observe smooth PAAS-normalized patterns with negative Ce anomaly, an increase from LREE to MREE, and a slight decrease from Tb to Lu, sometimes accompanied by a small positive Y/Ho anomaly. The calculated concentrations generally increase with depth. Paul et al (2019) previously described very similar distribution patterns for CCZ sediment pore water and suggested Mn and Fe phases as the REY source. The pore water REY patterns clearly differ from bottom seawater already in the first centimetres of surface sediment– this sharp shift demonstrates that the dissolved pore water REY pool in the sediment surface is controlled by fluid-mineral equilibria.

The DGT passive sampling method may provide an additional tool to investigate biogeochemical processes at the deep-sea sediment-water interface and in the open ocean, and to monitor effects of anthropogenic disturbances at the seafloor on benthic trace element fluxes. We will discuss uncertainties of concentration calculation resulting from diffusion coefficients and from non-steady state conditions in pore water, and the comparability of DGT-derived distribution pattern and concentrations with results from physically filtered water. The DGT labile fraction is thought to represent the bioavailable fraction of trace elements and may also include colloids and nanoparticles (NPCs).

 

Alibo and Nozaki, 1999: Geochimica et Cosmochimica Acta 63, pp. 363-372.

Paul et al, 2019: Geochimica et Cosmochimica Acta 251, pp. 56-72.

D2809 |
EGU2020-6215
Nikolay Nezlin, Mark Halverson, Jean-Michel Leconte, Igor Shkvorets, Eric Siegel, Rui Zhang, and Greg Johnson

This study analyses accuracy and stability of salinity measurements collected by four Argo autonomous drifters with RBR Ltd. inductive conductivity sensors operating in the Pacific Ocean during the recent 2-4 years. Inductive sensors have advantages over traditionally used electrode-type cells due to their better resistance to surface contamination and low power requirements, resulting in more robust and accurate measurements and extended float lifetimes.  Proper assessment of the quality of the data collected by autonomous drifters is challenging due to lack of reference information. An important part of Argo program is the Delayed-Mode Quality Control process including salinity drift analysis and correction using the ‘Owens-Wong Calibration’ (OWC) method based on objective mapping of available reference data. This method, however, can misinterpret imperfect reference data as sensor drift. In this study, analyzing OWC output we introduce a combination of visualization methods focused on the locations where reference data can be treated as problematic. These methods include the analysis of spatial locations of the ‘profile correction factor’ along the float trajectory, comparing reference salinity fields calculated by the OWC method to additional reference sources (climatologies) and comparative analysis of different floats operating in the same area using the same reference datasets. The results demonstrate high level of stability of inductive conductivity cells on Argo floats, making them promising alternative for traditionally used Argo float CTDs equipped with electrode-type conductivity sensors.

 

D2810 |
EGU2020-17071
Paolo Oliveri, SImona Simoncelli, Pierluigi DI Pietro, and Sara Durante

One of the main challenges for the present and future in ocean observations is to find best practices for data management: infrastructures like Copernicus and SeaDataCloud already take responsibility for assembly, archive, update and publish data. Here we present the strengths and weaknesses in a SeaDataCloud Temperature and Salinity time series data collections, in particular a tool able to recognize the different devices and platforms and to merge them with processed Copernicus platforms.

While Copernicus has the main target to quickly acquire and publish data, SeaDataNet aims to publish data with the best quality available. This two data repository should be considered together, since the originator can ingest the data in both the infrastructures or only in one, or partially in both. This results sometimes in data partially available in Copernicus or SeaDataCloud, with great impact for the researcher who wants to access as much data as possible. The data reprocessing should not be loaded on researchers' shoulders, since only skilled users in all data management plan know how merge the data.

The SeaDataCloud time series data collections is a Global Ocean soon-to-be-published dataset that will represent a reference for ocean researchers, released in binary, user friendly Ocean Data View format. The database management plan was originally for profiles, but had been adapted for time series, resolving several issues like the uniqueness of the identifiers (ID).

Here we present an extension of the SOURCE (Sea Observations Utility for Reprocessing. Calibration and Evaluation) Python package, able to enhance the data quality with redundant sophisticated methods and simplify their usage. 

SOURCE increases quality control (Q/C) performances on observations using statistical quality check procedures that follows the ocean best practices guidelines, exploiting the following  issues:

  1. Find and aggregate all broken time series using likeness in ID parameter strings;
  2. Find and organize in a dictionary all different metadata variables;
  3. Correct time series time to match simpler measure units;
  4. Filter devices that are outside of a selected horizontal rectangle;
  5. Give some information on original Q/C scheme by SeaDataCloud infrastructure;
  6. Give information tables on platforms and on the merged ID string duplicates together with an errors log file (missing time, depth, data, wrong Q/C variables, etc.).

In particular, the duplicates table and the log file may be helpful to SeaDataCloud partners in order to update the data collection and make it finally available for the users.

The reconstructed SeaDataCloud time series data, divided by parameter and stored in a more flexible dataset, give the possibility to ingest it in the main part of the software, allowing to compare it with Copernicus time series, find the same platform using horizontal and vertical surroundings (without looking to ID) find and cleanup  duplicated data, merge the two databases to extend the data coverage.

This allow researchers to have the most wide and the best quality possible data for the final users release and to to use these data to calibrate and validate models, in order to reach an idea of a whole area sea conditions.

D2811 |
EGU2020-18477
Raul Bardaji, Jaume Piera, Juanjo Dañobeitia, and Ivan Rodero

In marine sciences, the way in which many research groups work is changing as scientists use published data to complement their field campaign data online, thanks to the large increase in the number of open access observations. Many institutions are making great efforts to provide the data following FAIR principles (findability, accessibility, interoperability, and reusability) and are bringing together interdisciplinary teams of data scientists and data engineers.

There are different platforms for downloading marine and oceanographic data and many libraries to analyze data. However, the reality is that scientists continue to have difficulty finding the data they need. On many occasions, data platforms provide information about the metadata, but they do not show any underlying graph of the data that can be downloaded. Sometimes, scientists cannot download only the data parameters of interest and have to download huge amounts of data with other not useful parameters for their studies. On other occasions, the platform allows to download the data parameters of interest but offers the time-series data as many files, and it is the scientist who has to join the pieces of data into a single dataset to be analyzed correctly. EMSO ERIC is developing a data service that helps reduce the burden of scientists to search and acquire data as much as possible.

 

We present the EMSO ERIC DataLab web application, which provides users with capabilities to preview harmonized data from the EMSO ERIC observatories, perform some basic data analyses, create or modify datasets, and download them. Use case scenarios of the DataLab include the creation of a NetCDF file with time-series information across EMSO ERIC observatories.

The DataLab has been developed using engineering best practices and trend technologies for big data management, including specialized Python libraries for web environments and oceanographic data analysis, such as Plotly, Dash, Flask, and the Module for Ocean Observatory Data Analysis (MOODA).

D2812 |
EGU2020-6737
Il-Nam Kim, Seong-Su Kim, Ki-Tae Park, and Jae-Hyun Lim

 Gas chromatography (GC) is the most commonly used analytical equipment for tracer gas measurements. However, high performance equipment such as cavity ring-down spectrometer (CRDS) has been developed and currently become commercially available (G2308, PICARRO). CRDS is optical spectrometer to measure tracer gas, and its principal is that determines the gas concentration through the rate of decay of the optical signal. The great advantage of using CRDS is that not required too many material, time, and easy to handle than GC system. In general, CRDS is used for continuous measurement, which requires a large amount of gas for quantification. So, we have modified CRDS system to measure small amount of N2O/CH4 gases which is extracted from seawater samples using headspace method, and in turn have tested in various marine environments from coastal regions to open oceans. As a result, we have obtained highly accurate concentrations of dissolved N2O & CH4 gases, suggesting that the system would be useful to study dynamics of climate-relevant trace gases.

D2813 |
EGU2020-22606
Scott M. Brown, Christopher J. Zappa, Nathan J. M. Laxague, Tejendra Dhakal, Ryan A. Harris, Aaron Farber, and Ajit Subramaniam

Unmanned aerial vehicles (UAVs) are proving to be an important modern sensing platform that supplement the sensing capabilities from platforms such as satellites, aircraft, research vessels, moorings, and gliders. UAVs, like satellites and aircraft can provide a synoptic view of a relatively large area. However, the coarse resolution provided by satellites and the operational limitations of manned aircraft has motivated the development of unmanned systems. UAVs offer unparalleled flexibility of tasking; for example, low altitude flight and slow airspeed allow for the characterization of a wide variety of geophysical phenomena at the ocean surface and in the marine atmospheric boundary layer. Here, we present the development of cutting-edge payload instrumentation for UAVs that provides a new capability for ship-deployed operations to capture a unique, high resolution spatial and temporal variability of the changing air-sea interaction processes than was previously possible. The modular design of the base payload means that new instruments can be incorporated into new research proposals that may include new instruments for expanded use of the payloads as a long-term research facility. Additionally, we implement a novel capability for vertical take-off and landing (VTOL) from research vessels. This VTOL capability is safer and requires less logistical support than previous ship-deployed systems. Furthermore, these VTOL UAV systems have 15-hour endurance with 15-lb payloads, fully autonomous take-off, flight, and landing from ships, and high-bandwidth data telemetry (100 Mbits/s over 50+ nm range) for real-time mission control and provide for our “eyes over the horizon.” The payloads developed include thermal infrared, visible broadband and hyperspectral, and near-infrared hyperspectral high-resolution imaging. Additional capabilities include quantification of the longwave and shortwave hemispheric radiation budget (up- and down-welling) as well as direct air-sea turbulent fluxes. Finally, a UAV-deployed dropsonde-microbuoy was developed in order to profile the temperature, pressure and humidity of the atmosphere and the temperature and salinity of the near-surface ocean. These technological advancements provide the next generation of instrumentation capability for UAVs. We present on the results of 3 case studies in the South Pacific near Fiji, including measurements characterizing meso-scale ocean SST fronts, trichodesmium blooms, and floating pumice rafts from a recent undersea volcanic eruption near Tonga. When deployed from research vessels, these UAVs will provide a transformational science prism unequaled using 1-D data snapshots from ships or moorings alone.