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Below the surface of the ocean, currents, eddies, and other physical processes redistribute energy and biologically important elements. Measuring this transport can be challenging, and scientists must address a wide spectrum of oceanographic and engineering concepts when designing instruments to observe these processes. In this activity, high-school aged students are asked to consider some of these challenges by using easily-available material to design, assemble, and test their own simple deep-water floats, mimicking a tool used by oceanographers to measure transport below the ocean's surface. Students are asked to build floats that are neutrally buoyant at an interface between oil and water, teaching them key oceanographic concepts such as buoyancy and ocean stratification. Additionally, students manage a budget by selecting cost-effective materials to construct their floats. This activity aims to increase students' understanding of how ocean currents affect our planet's climate and ecosystems, how we observe these phenomena, and some of the practical challenges that oceanographers face. The project supports key educational standards and aims to deepen students' appreciation for marine science. [ABSTRACT FROM AUTHOR]

Over the last 30 years, ocean sciences have been undergoing a technological revolution. Changes include the transition of autonomous platforms from being interesting engineering projects to being critical tools for scientists studying a range of processes at sea. My career has benefitted immensely from these technical innovations, allowing me to be at sea (virtually) 365 days a year and operate ocean networks globally. While these technical innovations have opened many research doors, many aspects of oceanography are unchanged. In my experience, working/talking/scheming with scientists is most effective face-to-face. Despite the growing capabilities of robotic platforms, we will still need to go to sea on ships to conduct critical experiments. As the responsibilities of scientists expand with mandated outreach efforts, I strongly urge young scientists to leverage the expertise of Broader Impact professionals, who are increasingly available to our community, in order to maximize the effectiveness and efficiency of our outreach efforts. Given the increasing observations of change occurring in the ocean, our work is ever-more important while still being fun. I am blessed to have had a career as an oceanographer exploring this planet. [ABSTRACT FROM AUTHOR]

Few observational platforms are able to sustain direct measurements of all the key variables needed in the bulk calculation of air‐sea carbon dioxide (CO2) exchange, a capability newly established for some Uncrewed Surface Vehicles (USVs). Western boundary currents are particularly challenging observational regions due to strong variability and dangerous sea states but are also known hot spots for CO2 uptake, making air‐sea exchange quantification in this region both difficult and important. Here, we present new observations collected by Saildrone USVs in the Gulf Stream during the winters of 2019 and 2022. We compared Saildrone data across co‐located vehicles and against the Pioneer Array moorings to validate the data quality. We explored how CO2 flux estimates differ when all variables needed to calculate fluxes from the bulk formulas are simultaneously measured on the same platform, relative to the situation where in situ observations must be combined with publicly‐available data products. We systematically replaced variables in the bulk formula with those often used for local and regional flux estimates. The analysis revealed that when using the ERA‐5 reanalysis wind speed in place of in situ observations, the ocean uptake of CO2 is underestimated by 8%; this underestimate grows to 9% if the NOAA Marine Boundary Layer atmospheric CO2 product and ERA‐5 significant wave height are also used in place of in situ observations. Overall our findings point to the importance of collecting contemporaneous observations of wind speed and ocean pCO2 to reduce biases in estimates of regional CO2 flux, especially during high wind events. Plain Language Summary: The North Atlantic Ocean absorbs a large amount of carbon dioxide (CO2) from the atmosphere. The ocean CO2 uptake mainly occurs during the winter months in a region where a swift ocean current, called the Gulf Stream, carries warm waters from the tropics to northern latitudes. Understanding how much CO2 this ocean region absorbs is important for constraining global scale assessments of the sources and sinks of CO2. In this paper, we reflect on the methods that are typically used to calculate the exchange of CO2 between the ocean and atmosphere. Using new data collected by uncrewed surface vehicles, that resemble small sailboats, in the North Atlantic Ocean in the vicinity of the Gulf Stream, we find that the estimate of the exchange of CO2 is larger when directly measured wind speeds are used in the calculation in comparison to wind speeds from a widely used data product. This result signifies the importance of co‐located sensors on the same observing platform. Key Points: Compared to Saildrone wind speeds, the ERA‐5 reanalysis appears to underestimate the highest wind speed events (>10 m s−1)Co‐located ocean pCO2 and wind speed observations results in larger uptake of CO2 in this region by 9%Using a sea‐state dependent gas transfer velocity leads to a 28% greater ocean uptake of CO2 compared to using a wind‐only equation [ABSTRACT FROM AUTHOR]

In the boreal summer of 2021, the equatorial Atlantic experienced the strongest warm event, that is, Atlantic Niño, since the beginning of satellite observations in the 1970s. Such events have far‐reaching impacts on large‐scale wind patterns and rainfall over the surrounding continents. Yet, developing a paradigm of how Atlantic Niño interacts with the upper‐ocean currents and intraseasonal waves remains elusive. Here we show that the equatorial Kelvin wave associated with the onset of the 2021 Atlantic Niño modulated both the background flow and the eddy flux of the equatorial upper‐ocean circulation, causing an extremely weak and delayed tropical instability wave (TIW) season. TIW‐induced variations of sea surface temperature (SST), sea surface salinity, sea surface height, and eddy temperature advection were exceptionally weak during May to July, the climatological peak of TIW activity, but rebounded in August when higher than normal variability was observed. Moored velocity data at 23°W show that during the peak of the 2021 Atlantic Niño from June to August, the Equatorial Undercurrent was deeper and stronger than usual. An anomalously weak eddy momentum flux strongly suppressed barotropic energy conversion north of the equator from May to July, likely contributing to low TIW activity. Reduced baroclinic energy conversion also might have played a role, as the meridional gradient of SST was sharply reduced during the Atlantic Niño. Despite extremely weak TIW velocities, modest intraseasonal variability of chlorophyll‐a (Chl‐a) was observed during the Atlantic Niño, due to pronounced meridional Chl‐a gradients that partly compensated for the weak TIWs. Plain Language Summary: Every few years the eastern equatorial Atlantic Ocean is significantly warmer than usual during boreal summer. Such warm events are referred to as Atlantic Niño events, and share similarities with El Niño events in the Pacific. In 2021, the strongest Atlantic Niño in at least four decades was observed in the equatorial Atlantic. This study is the first that investigates the complex interaction between Atlantic Niño, tropical Atlantic upper‐ocean currents, and equatorial waves based on various observational data sets. We show that the developing 2021 Atlantic Niño weakened both the background flow and the variability of near‐surface currents in May, which in turn largely reduced the strength of intraseasonal (20–50 days) waves that are usually generated by instability of the upper‐ocean zonal currents. As a consequence, the cooling effect that these waves usually have north of the equator and the warming effect along the equator vanished from May to July 2021. Interestingly, variability of chlorophyll concentration was enhanced, suggesting that enhanced meridional chlorophyll gradients compensated for reduced wave activity. Key Points: The developing 2021 Atlantic Niño led to weaker equatorial surface currents and reduced vertical shear of upper‐ocean horizontal velocityStrong reduction of the surface flow, eddy flux, and meridional temperature gradient in May caused extremely weak and delayed tropical instability wave (TIW) seasonReduced meridional TIW advection contributed to sharpen the north equatorial Chl‐a front resulting in modest intraseasonal Chl‐a variability [ABSTRACT FROM AUTHOR]

The Atlantic meridional overturning circulation (AMOC) is a large-scale circulation pattern responsible for northward heat transport in the Atlantic and is associated with climate variations on a wide range of time scales. Observing the time-varying AMOC has fundamentally changed our understanding of the large-scale ocean circulation and its interaction with the climate system, as well as identified shortcomings in numerical simulations. With a wide range of gains already achieved, some now ask whether AMOC observations should continue. A measured approach is required for a future observing system that addresses identified gaps in understanding, accounts for shortcomings in observing methods and maximizes the potential to guide improvements in ocean and climate models. Here, we outline a perspective on future AMOC observing and steps that the community should consider to move forward. This article is part of a discussion meeting issue 'Atlantic overturning: new observations and challenges'. [ABSTRACT FROM AUTHOR]

The high-resolution expendable bathythermograph (HR-XBT) network measures temperature down to approximately 800 m along fixed transects. In comparison, Argo floats are distributed throughout the global ocean and measure temperature and salinity down to approximately 2000 m. Over the 2004-2019 period, the HR-XBT network tended to have a greater sampling density near the coast, while Argo sampling density was generally equivalent to, or greater than, the HR-XBT network in the ocean interior. To take advantage of the benefits of each of these observing systems, a method for combining measurements from HR-XBT, Argo, and satellite altimetry observations was implemented. This method produced estimates of geostrophic velocity and transport in the upper 800 m normal to the HR-XBT transects in the Indian and Pacific Oceans over an approximately 16 year period at high spatial (0.1° along-transect spacing) and temporal (1 month) resolutions. The combined method better resolved the mean geostrophic velocity and transport in the western boundary currents and their recirculations compared to estimates from a 2004-2018 mean high-resolution climatology computed using only Argo data. An additional benefit of the combined method is that it provides a monthly time series of velocity and transport for each HR-XBT transect. This monthly time series captures the temporal variability and will allow for examination of possible drivers of ocean transport.

The tragic accident of the Macondo platform operated by British Petroleum (BP) unleashed in 2010 one of the largest oil spills in history, lasting over three months, spilling nearly 500 million liters of oil in one of the most biodiverse ocean regions. This accident revealed the technological deficiencies for the control of a spill in deep waters of the hydrocarbon industry. Simultaneously it showed important gaps in knowledge to predict the propagation and fate of the large volumes of hydrocarbons at depth and on the surface ocean and, more importantly, on their impact on the great ecosystem of the Gulf of Mexico. The necessity to understand and predict the transport, fate and ecosystem-level impacts of large oil spills in the southern Gulf of Mexico, a key region for oil exploration and extraction, led policymakers, scientists, and industry representatives from PEMEX (the Mexican oil company) to jointly launch an ocean observation project (2015-22) aimed to provide a multi-layered environmental baseline, develop a modern monitoring and computational modeling capacity and promote scientific understanding of the marine environment throughout the Mexican Exclusive Economic Zone (EEZ). The initiative, led by the Research Consortium for the Gulf of Mexico (CIGoM), brought together more than 300 multidisciplinary researchers from more than a two dozen institutions in Mexico and abroad, including the Centre for Scientific Research and Higher Education of Ensenada (CICESE) as the leading institution, the National Autonomous University of Mexico (UNAM), the Centre for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) in Mérida, the Autonomous University of Baja California (UABC), and the Centre for Engineering and Industrial Development (CIDESI). Financial support was provided by the National Council for Science and Technology and the Ministry of Energy Hydrocarbon Fund.

Tropical Instability Waves (TIWs) are the dominant source of intraseasonal variability in the central equatorial Atlantic and play an important role in the redistribution of heat in the upper ocean. Here we use multidecadal records of sea surface temperature, sea level anomaly, sea surface salinity, and near‐surface currents constructed from in situ and satellite observations to reveal a long‐term intensification of the intraseasonal variability of these variables due to an increase of TIW activity. Enhanced barotropic energy conversion from increased covariance of horizontal current fluctuations, rather than low‐frequency changes of the mean zonal currents, drives the TIW intensification. As a consequence, boreal summer cooling of tropical North Atlantic surface waters through horizontal eddy temperature advection increased by 0.03°C month−1 decade−1 during 1993–2021, a change of 74% ± 53% relative to the long‐term mean. The presented multidecadal TIW trends are strongly modulated by interannual variations like the 2021 Atlantic Niño. Plain Language Summary: In the equatorial Atlantic, temperature, salinity, sea level anomaly, and ocean velocity variations on time scales of tens of days are dominated by the presence and westward passage of large‐scale Tropical Instability Waves (TIWs). Several decades of satellite and surface drifter data as well as moored velocity observations show a long‐term intensification of TIW activity in all of these variables in the tropical North Atlantic where TIWs are most pronounced. We find that increased high‐frequency flow variability, and not long‐term changes of the mean zonal current system, drives the TIW intensification. One consequence of increased Atlantic Ocean TIW activity is the corresponding intensification of the horizontal eddy temperature advection pattern in boreal summer leading to stronger cooling of surface waters north of the equator. This equates to an increase in TIW‐driven sea surface temperature cooling of 74% ± 53% in the tropical North Atlantic during the last 3 decades. The presented multidecadal TIW trends are strongly modulated by interannual variations such as the 2021 Atlantic Niño. We further explore potential large‐scale drivers of the TIW intensification, including changes in high‐frequency wind variability. Key Points: In situ and satellite observations show a long‐term intensification of Tropical Instability Waves (TIWs) in the tropical North AtlanticEnhanced TIW activity is mainly due to increased barotropic instability associated with increased covariance of velocity fluctuationsAs a result, TIW‐driven sea surface cooling north of the equator due to eddy temperature advection has increased by 74% from 1993 to 2021 [ABSTRACT FROM AUTHOR]

Zooplankton play a key role in marine food webs and carbon cycling and are useful indicators of climaterelated changes and ocean health in pelagic ecosystems. Zooplankton are traditionally identified to species through microscopy, but new molecular techniques have enabled the identification of individual specimens (DNA barcoding) or multiple species in the same sample (DNA metabarcoding). Metabarcoding has been tested and refined using zooplankton collected in South African waters for the first time. Challenges to the implementation of DNA-based methods to measure zooplankton biodiversity easily and routinely include an incomplete DNA barcode reference library, logistical complexity and uptake of the new technology by environmental management agencies. These challenges call for a national effort to intensify zooplankton barcoding initiatives and to effectively engage stakeholders in developing a roadmap towards application of DNA-based methods in marine environmental management. Significance: • Metabarcoding has been successfully applied to marine zooplankton for the first time in South Africa, demonstrating its potential as a tool to generate ecosystem indicators during routine ocean observations. • National barcoding efforts must be intensified to provide a comprehensive reference library of zooplankton DNA. • Effective engagement with stakeholders is required to overcome logistical and policy challenges, and to provide a roadmap towards application of DNA-based methods in marine environmental management. [ABSTRACT FROM AUTHOR]

In today's world where there Is an Increasing need to monitor and understand our changing oceans, under flat or shrinking budgets, It Is challenging for a single organization to tackle problems of this scale and magnitude alone. Engineers and scientists from the National Oceantic and Atmospheric Administration's National Data Buoy Center (NDBC) and the Monterey Bay Aquarium Research Institute (MBARI) began a collaboration with this challenge in mind. The collaboration took advantage of each organization's strengths: MBARI has the capability to rapidly develop new instrument systems, and NDBC has the infrastructure on which to test their capabilities in the field. Here, we present development efforts that led to the deployment of a small partial pressure of carbon dioxide (pCO2) sensor system developed by MBARI on an NDBC buoy. The overarching goal was to demonstrate the utility of NDBC's new Auxiliary (Aux) module and determine the ease of adding third- party instrumentation to NDBC buoys. The Aux module is part of NDBC's latest generation of weather buoy data acquisition and reporting system, which provides more modularity and flexibility over previous systems. Given the large number of NDBC buoys currently in service, this capability opens up the possibility of a dense array of low-cost sensors to complement more highly specialized expensive mooring systems that are sparsely distributed. The partnership process led to the successful deployment of the pCO2 system on NDBC buoy 46013 off Bodega Bay, California, about 48 nautical miles northwest of San Francisco, for over a year of unattended operation. The technical and scientific results are described. [ABSTRACT FROM AUTHOR]

Direct observations of the oceans acquired on oceanographic research ships operated across the international community support fundamental research into the many disciplines of ocean science and provide essential information for monitoring the health of the oceans. A comprehensive knowledge base is needed to support the responsible stewardship of the oceans with easy access to all data acquired globally. In the United States, the multidisciplinary shipboard sensor data routinely acquired each year on the fleet of coastal, regional and global ranging vessels supporting academic marine research are managed by the Rolling Deck to Repository (R2R, rvdata.us) program. With over a decade of operations, the R2R program has developed a robust routinized system to transform diverse data contributions from different marine data providers into a standardized and comprehensive collection of global-ranging observations of marine atmosphere, ocean, seafloor and subseafloor properties that is openly available to the international research community. In this article we describe the elements and framework of the R2R program and the services provided. To manage all expeditions conducted annually, a fleet-wide approach has been developed using data distributions submitted from marine operators with a data management workflow designed to maximize automation of data curation. Other design goals are to improve the completeness and consistency of the data and metadata archived, to support data citability, provenance tracking and interoperable data access aligned with FAIR (findable, accessible, interoperable, reusable) recommendations, and to facilitate delivery of data from the fleet for global data syntheses. Findings from a collection-level review of changes in data acquisition practices and quality over the past decade are presented. Lessons learned from R2R operations are also discussed including the benefits of designing data curation around the routine practices of data providers, approaches for ensuring preservation of a more complete data collection with a high level of FAIRness, and the opportunities for homogenization of datasets from the fleet so that they can support the broadest re-use of data across a diverse user community.

Zooplankton play a key role in marine food webs and carbon cycling and are useful indicators of climaterelated changes and ocean health in pelagic ecosystems. Zooplankton are traditionally identified to species through microscopy, but new molecular techniques have enabled the identification of individual specimens (DNA barcoding) or multiple species in the same sample (DNA metabarcoding). Metabarcoding has been tested and refined using zooplankton collected in South African waters for the first time. Challenges to the implementation of DNA-based methods to measure zooplankton biodiversity easily and routinely include an incomplete DNA barcode reference library, logistical complexity and uptake of the new technology by environmental management agencies. These challenges call for a national effort to intensify zooplankton barcoding initiatives and to effectively engage stakeholders in developing a roadmap towards application of DNA-based methods in marine environmental management. Significance: • Metabarcoding has been successfully applied to marine zooplankton for the first time in South Africa, demonstrating its potential as a tool to generate ecosystem indicators during routine ocean observations. • National barcoding efforts must be intensified to provide a comprehensive reference library of zooplankton DNA. • Effective engagement with stakeholders is required to overcome logistical and policy challenges, and to provide a roadmap towards application of DNA-based methods in marine environmental management.

Arctic observations are becoming increasingly valuable as researchers investigate climate change and its associated concerns, such as decreasing sea ice and increasing ship traffic. Networks of sensors with frequent sampling capabilities are needed to run forecast models, improve navigation, and inform climate research. Sampling frequency and deployment duration are currently constrained by battery power limitations. In-situ power generation using marine renewable energy sources such as waves and currents can be used to circumvent this constraint. Wave and current resources vary spatially and temporally in the Arctic, with some locations and seasons being better suited for marine renewable energy power generation. Locations and seasons with small resources may still be able to use marine renewable energy because of the low power requirements of the instruments. In this study, we describe the wave and current resources in the Arctic, outline the electricity generation developments that are needed to utilize the resources, and suggest use cases. Wave and current energy converters developed to power observations in the Arctic could also be used to power observations at lower latitudes. Marine renewable energy has the potential to decrease dependence on batteries and improve data collection capabilities in the Arctic; however, this would require the development of new low power technologies that can operate in extreme Arctic environments.

Based on velocity data from a long‐term moored observatory located at 0°N, 23°W we present evidence of a vertical asymmetry during the intraseasonal maxima of northward and southward upper‐ocean flow in the equatorial Atlantic Ocean. Periods of northward flow are characterized by a meridional velocity maximum close to the surface, while southward phases show a subsurface velocity maximum at about 40 m. We show that the observed asymmetry is caused by the local winds. Southerly wind stress at the equator drives northward flow near the surface and southward flow below that is superimposed on the Tropical Instability Wave (TIW) velocity field. This wind‐driven overturning cell, known as the Equatorial Roll, shows a distinct seasonal cycle linked to the seasonality of the meridional component of the south‐easterly trade winds. The superposition of vertical shear of the Equatorial Roll and TIWs causes asymmetric mixing during northward and southward TIW phases. Plain Language Summary: Tropical Instability Waves (TIWs) are clear in satellite measurements of sea surface temperature as horizontal undulations with wavelength of the order of 1,000 km in equatorial regions of both Atlantic and Pacific Oceans. TIWs are characterized by their distinctive upper‐ocean meridional velocity structure. TIWs amplify vertical shear and thus contribute to the generation of turbulence which in turn leads to the mixing of heat and freshwater downward into the deeper ocean. In this study we show that the prevailing southerly winds in the central equatorial Atlantic drive near‐surface northward and subsurface southward flows, which are superposed on the meridional TIW velocity field. The strength of this wind driven cell is linked to the seasonal cycle of the northward component of the trade winds, peaking in boreal fall when TIWs reach their maximum amplitude. The overturning cell affects the vertical structure of the meridional velocity field and thus has impact on the generation of current shear and turbulence. We show that the overturning reduces/enhances shear during northward/southward TIW flow, an asymmetry that is consistent with independent measurements showing asymmetric mixing. Key Points: Composites of Tropical Instability Waves at 0°N, 23°W show a surface (subsurface) velocity maximum during northward (southward) phasesMeridional wind stress forces a seasonally‐varying, shallow cross‐equatorial overturning cell‐the Equatorial RollThe superposition of Tropical Instability Waves and Equatorial Roll causes asymmetric mixing during north‐ and southward phases [ABSTRACT FROM AUTHOR]

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A yearlong wind and wave dataset derived from a cost-effective GPS wave buoy (Spotter) is compared to waves obtained from an accelerometer wave buoy (Datawell) and winds obtained from a collocated meteorological buoy. Overall, there was a strong correlation in bulk wave parameters obtained from the Spotter buoy and the Datawell buoy (RMSE of 0.06 m, 0.27 s, and 21.89° for significant wave height, mean wave period, and peak wave direction, respectively). Similarly, the bulk characteristics compared well when separating the directional wave spectra into sea and swell components with more scatter in mean wave periods for lower frequencies. Measurements of mean directional spread from the Spotter buoy were 7.51° larger than the Datawell, spreading more wave energy across different directions outside the peak direction. Additional analysis indicates that the increased directional spreading arises from a bias in the a1 and b1 spectral moments. Using the equilibrium frequency range of the wave energy spectrum, the Spotter buoy can derive wind speed and direction. This study found the Spotter buoy can report wind speed and direction with reasonable accuracy but underestimates wind speeds less than 4 m/s and greater than 8 m/s and was less accurate reporting wind directions oriented offshore. A comparison with a Spotter buoy in deeper water revealed the Spotter buoy further offshore was most accurate in reporting wind directions indicating this proxy-based measurement of wind speed and wind direction may be significantly influenced by fetch and local geography (e.g., large-scale cuspate coastlines).

Subtropical western boundary currents (WBCs) exert a substantial influence on regional climate. To improve WBC observations on seasonal‐to‐decadal timescales, and characterize their subsurface structure to 1975 m depth, we combine high‐resolution expendable bathythermograph, Argo, and satellite altimetry observations in the Agulhas Current, East Australian Current, and Kuroshio. The resulting 16 year time series (2004–2019) show a weakening trend in Kuroshio transport, but no trend in Agulhas transport or East Australian Current transport. All three WBCs have stronger transport in summer, driven mostly by changes in current speed rather than current width. This unique subsurface view of WBC variability reveals changes in the path of the Kuroshio Extension on interannual timescales, and eddy variability in the Agulhas. Our work highlights how this application of a consistent methodology to combine complementary ocean observations allows for an unprecedented direct comparison of variability between WBCs. Plain Language Summary: Western boundary currents are major ocean currents located on the western side of the world's oceans. These currents transport warm water toward the poles, which influences regional weather and climate. However, despite their importance, the fast speeds, high variability, and narrow width of these currents makes them difficult to observe. Here we examine the western boundary currents (WBCs) of the Indian Ocean (Agulhas Current) and Pacific Ocean (East Australian Current and Kuroshio) using measurements from three different ocean observing networks. The same method is applied to each current, allowing us to compare variability in the three currents. Between the start of 2004 and end of 2019 we find that transport of water has decreased in the Kuroshio but has not changed in the Agulhas or East Australian Current. We find changes in the path of the Kuroshio on interannual time scales, and shorter and irregular changes in the path of the Agulhas. On annual time periods, all three currents transport more water in summer than winter, which is related to faster speeds during the summer. These long subsurface time series can help us better understand how WBC variability impacts society at the western boundaries of the ocean. Key Points: Combining ocean observations allows estimation of western boundary current (WBC) variability between 0 m and 1975 m depth over 2004–2019A decrease was observed in Kuroshio transport, no significant change was observed in Agulhas or East Australian Current transportTransport in all three WBCs is greatest in summer and related to coincident changes in core speed [ABSTRACT FROM AUTHOR]

Water mass transformation in the Southern Ocean is vital for driving the large‐scale overturning circulation, which transports heat from the surface to the ocean interior. Using profiling gliders, this study investigates the role of summertime buoyancy forcing and wind‐driven processes on the intraseasonal (1–10 days) mixed layer thermohaline variability in three Southern Ocean regions southwest of Africa important for water mass transformation—the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ), and Marginal Ice Zone (MIZ). At intraseasonal time scales, heat flux was shown as the main driver of buoyancy gain in all regions. In the SAZ and MIZ, shallow mixed layers and strong stratification enhanced mixed layer buoyancy gain by trapping incoming heat, while buoyancy loss resulted primarily from the entrainment of cold, salty water from below. In the PFZ, rapid mixing linked to Southern Ocean storms set persistently deep mixed layers and suppressed mixed layer intraseasonal thermohaline variability. In the polar regions, lateral stirring of meltwater from seasonal sea‐ice melt dominated daily mixed layer salinity variability. We propose that these meltwater fronts are advected to the PFZ during late summer, indicating the potential for seasonal sea‐ice freshwater to impact a region where the upwelling limb of overturning circulation reaches the surface. This study reveals a regional dependence of how the mixed layer thermohaline properties respond to small spatiotemporal processes, emphasizing the importance of surface forcing occurring between 1 and 10 days on the mixed layer water mass transformation in the Southern Ocean. Plain Language Summary: The Southern Ocean extends from the cold and fresh polar waters near Antarctica to the warm and salty subtropics and is capped by a region called the mixed layer, where winds keep properties well mixed. Mixed layer waters play a key role in the Earth's climate by taking up heat from the atmosphere before being transported into the ocean interior, where they remain for centuries. The process by which heat leaves the mixed layer is poorly understood, but recent observations suggest that oceanic currents that vary on the scale of a few kilometers, that are not represented well in climate models, may dominate this exchange. Using autonomous ocean gliders at three locations from the northern to the southern Southern Ocean, we show that in the Subantarctic and sea‐ice‐impacted sea, shallow mixed layers lead to increased warming by trapping incoming heat from the atmosphere, while winds simultaneously mix up colder, saltier water from below. North of the sea‐ice‐impacted ocean, mixing by strong winds throughout the summer reduces mixed layer warming. Our findings show how mixed layer conditions within the Southern Ocean respond to daily weather variability, improving our understanding of how the ocean responds to the atmosphere above. Key Points: Regional glider missions reveal 1–10 day mixed layer variability in the Subantarctic, Polar, and sea‐ice impacted Southern OceanSurface heating drives buoyancy gain in all regions, while entrainment leads to buoyancy loss in the Subantarctic and Marginal Ice ZoneIn the Polar Frontal Zone, deep mixing by storms suppresses intraseasonal thermohaline variability [ABSTRACT FROM AUTHOR]

The quality control (QC) of ocean observational data, essential to establish a high-quality global ocean database, is one of the basic data pre-processing steps in oceanography research, marine monitoring, and forecasting. With the introduction of various advanced instruments in recent decades, oceanographic surveys have expanded from coastal regions to open oceans. However, as ocean in-situ observations are obtained using different instruments that offer heterogeneous data qualities, it is paramount that bad data could be accurately and efficiently identified via QC to provide a reliable global ocean database. In this review, we briefly summarize the latest progress of QC for oceanic in-situ observations, and mainly focus on temperature and salinity data. The similarities and differences between QC schemes developed by various ocean organizations are introduced. We also discuss the performances of the various QC schemes and identify the key challenges. Based on the discussions, several recommendations are proposed for future improvements in the QC for ocean observations. [ABSTRACT FROM AUTHOR]

The Yellow Sea is the most fog-prone region of the East Asian marginal seas. Since sea fog is caused due to complex interactions between atmospheric and oceanic environments, direct observations can help understand the physical processes involved in fogging over the oceans. Completed in 2014, the Socheongcho Ocean Research Station (S-ORS) plays a critical role in monitoring air-sea interactions over the Yellow Sea. This study aimed to evaluate the conditions favorable for fog generation and the physical processes underlying it using a suite of observations and turbulent heat flux data from S-ORS. First, we used the visibility data from S-ORS to quantify the frequency of sea fog over the Yellow Sea. From April to June 2016, sea-fog occurred 61 times, with a maximum duration of 135 h (approximately 5.6 days). Next, to understand the origin and characteristics of air mass associated with fog events, we classified the primary airflow paths in the region using a Hybrid Single-Particle Lagrangian Integrated Trajectory model. Among the four clusters identified from the cluster analysis, the third and fourth had distinct physical properties characteristic of cold and warm fog, respectively. The third cluster was characterized by relatively weak or negative heat advection and weak vertical mixing, while the fourth one featured strong positive heat transport and moisture convergence over the Yellow Sea. Finally, based on cluster analysis, we choose the representative cases related to these two clusters observed at S-ORS and compared the characteristics of turbulent air-sea fluxes associated with fog formations.

A regional assessment of three global ocean reanalysis products is presented for southern Africa’s major oceanographic features. The reanalyses include Mercator Ocean’s Global Reanalysis (GLORYS), the Commonwealth Scientific and Industrial Research Organisation’s (CSIRO) Bluelink Reanalysis (BRAN) and the Fleet Numerical Meteorology and Oceanography Center’s (FNMOC) global Hybrid Coordinate Ocean Model (HYCOM) reanalysis. The aim is to provide modelers with sufficient information for selecting the appropriate product for use as boundary conditions to force their regional ocean models, as well as to provide marine industries, relevant government agencies and academics with insight into the optimal reanalysis product for their purposes. The reanalyses are compared to both assimilated and independent observational datasets spanning various regions within the southern African marine environment. While all reanalysis products reproduce the eastern and western boundary current systems surrounding southern Africa, limitations exist. BRAN outperforms the other reanalyses in its representation of the Mixed Layer Depth, contributing to its good representation of coastal SSTs in the Benguela upwelling system, whereas GLORYS and HYCOM’s misrepresented MLD result in significant warm biases in this region. The Angola-Benguela Frontal Zone and it’s variability is best reproduced by BRAN and HYCOM. The Agulhas Current system’s major components are well reproduced by both GLORYS and BRAN. HYCOM, however, simulates considerably more early retroflections than are observed which have resulted in its mean eastward location. While all the reanalyses overestimate the occurrence of Agulhas meanders, GLORYS and BRAN resolve the associated variability best. Agulhas Current transport is best resolved by GLORYS, unlike BRAN and HYCOM which largely overestimate the magnitude of its south-westward flow, linked to their misrepresentation of the Current’s vertical structure. The bay-scale and nearshore evaluations highlighted issues pertaining to the resolution of the reanalyses and their use at such a small scale. The reanalyses are limited by their resolution, as well as by their misrepresentation of submesoscale processes or lack thereof, prompting the need for the development of regional downscaled models in and around the southern African oceans based on the global ocean reanalysis products.

Biomolecular ocean observing and research is a rapidly evolving field that uses omics approaches to describe biodiversity at its foundational level, giving insight into the structure and function of marine ecosystems over time and space. It is an especially effective approach for investigating the marine microbiome. To mature marine microbiome research and operations within a global ocean biomolecular observing network (OBON) for the UN Decade of Ocean Science for Sustainable Development and beyond, research groups will need a system to effectively share, discover, and compare “omic” practices and protocols. While numerous informatic tools and standards exist, there is currently no global, publicly-supported platform specifically designed for sharing marine omics [or any omics] protocols across the entire value-chain from initiating a study to the publication and use of its results. Toward that goal, we propose the development of the Minimum Information for an Omic Protocol (MIOP), a community-developed guide of curated, standardized metadata tags and categories that will orient protocols in the value-chain for the facilitated, structured, and user-driven discovery of suitable protocol suites on the Ocean Best Practices System. Users can annotate their protocols with these tags, or use them as search criteria to find appropriate protocols. Implementing such a curated repository is an essential step toward establishing best practices. Sharing protocols and encouraging comparisons through this repository will be the first steps toward designing a decision tree to guide users to community endorsed best practices.

Coastal ocean observing and modeling systems (coastal observatories), connected with regional and global ocean systems, improve the quality of information and forecasts for effective management of safe and sustainable maritime activities. The public availability of systematic and long-term information of the ocean is an engine for the Blue Economy, boosting economic growth, employment, and innovation. An overview of some Brazilian initiatives is presented in this paper, involving universities, private companies, federal and state agencies, covering institutions from south to north of Brazil. Although these initiatives focus mainly on ocean physics, integrated efforts can extend the scope to include biogeochemistry and marine biodiversity, helping to address interdisciplinary problems. Existing initiatives can be connected, and new ones fostered, to fill in the gaps of temporal and spatial coverage of ocean monitoring in the vast oceanic area under Brazilian jurisdiction (nationally referred to as the Blue Amazon, in reference to the similar richness of the Amazon Forest). The alignment among national and regional initiatives, as well as with international programs, can be promoted if coordinated by a national-level organization, maximizing the return of public investment and socioeconomic benefits. In light of international examples, possible future institutional arrangements are discussed, leveraging from existing national public policies and international cooperation that Brazil is taking part. The United Nations Decade of Ocean Science for Sustainable Development is a timely opportunity to encourage an institutional arrangement to support and articulate an integrated network of coastal observatories in Brazil.

Blue Maps aims to exploit the versatility of an ensemble data assimilation system to deliver gridded estimates of ocean temperature, salinity, and sea-level with the accuracy of an observation-based product. Weekly maps of ocean properties are produced on a 1/10°, near-global grid by combining Argo profiles and satellite observations using ensemble optimal interpolation (EnOI). EnOI is traditionally applied to ocean models for ocean forecasting or reanalysis, and usually uses an ensemble comprised of anomalies for only one spatiotemporal scale (e.g., mesoscale). Here, we implement EnOI using an ensemble that includes anomalies for multiple space- and time-scales: mesoscale, intraseasonal, seasonal, and interannual. The system produces high-quality analyses that produce mis-fits to observations that compare well to other observation-based products and ocean reanalyses. The accuracy of Blue Maps analyses is assessed by comparing background fields and analyses to observations, before and after each analysis is calculated. Blue Maps produces analyses of sea-level with accuracy of about 4 cm; and analyses of upper-ocean (deep) temperature and salinity with accuracy of about 0.45 (0.15) degrees and 0.1 (0.015) practical salinity units, respectively. We show that the system benefits from a diversity of ensemble members with multiple scales, with different types of ensemble members weighted accordingly in different dynamical regions.

A comparison between 4 (near) global ocean reanalysis products is presented for the waters around New Zealand. The objective is to provide information for an educated choice of ocean estate estimate. The simulations are compared to satellite and in situ observations, and vertical sections are extracted to evaluate the representation of the main regional boundary currents and their transport. Overall, the Copernicus GLORYS reanalysis exhibits the better performance, with more realistic ocean variability and smaller biases in the water column structure. However, the BlueLink Reanalysis (BRAN) provides more realistic transport estimates of the East Auckland Current, an important boundary current connecting New Zealand to the World Ocean. All simulations have important biases in both temperature and salinity, particularly in coastal regions. Moreover, they are not able to represent coastal currents and processes. Therefore, the present study results emphasise the need for a regional ocean reanalysis and a data assimilative operational forecast system. [ABSTRACT FROM AUTHOR]

The available historical oxygen data show that the deepest part of the South Adriatic Pit remains well-ventilated despite the winter convection reaching only the upper 700 m depth. Here, we show that the evolution of the vertical temperature structure in the deep South Adriatic Pit (dSAP) below the Otranto Strait sill depth (780 m) is described well by continuous diffusion, a continuous forcing by heat fluxes at the upper boundary (Otranto Strait sill depth) and an intermittent forcing by rare (several per decade) deep convective and gravity-current events. The analysis is based on two types of data: (i) 13-year observational data time series (2006–2019) at 750, 900, 1,000, and 1,200 m depths of the temperature from the E2M3A Observatory and (ii) 55 vertical profiles (1985–2019) in the dSAP. The analytical solution of the gravest mode of the heat equation compares well to the temperature profiles, and the numerical integration of the resulting forced heat equation compares favorably to the temporal evolution of the time-series data. The vertical mixing coefficient is obtained with three independent methods. The first is based on a best fit of the long-term evolution by the numerical diffusion-injection model to the 13-year temperature time series in the dSAP. The second is obtained by short-time (daily) turbulent fluctuations and a Prandtl mixing length approximation. The third is based on the zero and first modes of an Empirical Orthogonal Function (EOF) analysis of the time series between 2014 and 2019. All three methods are compared, and a diffusivity of approximately κ = 5 · 10−4m2s−1 is obtained. The eigenmodes of the homogeneous heat equation subject to the present boundary conditions are sine functions. It is shown that the gravest mode typically explains 99.5% of the vertical temperature variability (the first three modes typically explain 99.85%) of the vertical temperature profiles at 1 m resolution. The longest time scale of the dissipative dynamics in the dSAP, associated with the gravest mode, is found to be approximately 5 years. The first mode of the EOF analysis (85%) represents constant heating over the entire depth, and the zero mode is close to the parabolic profile predicted by the heat equation for such forcing. It is shown that the temperature structure is governed by continuous warming at the sill depth and deep convection and gravity current events play less important roles. The simple model presented here allows evaluation of the response of the temperature in the dSAP to different forcings derived from climate change scenarios, as well as feedback on the dynamics in the Adriatic and the Mediterranean Sea.

Marine renewable energy (MRE) encompasses the harvest of energy from the movement of ocean waters in the form of either currents or waves, as well as temperature and salinity differentials. To date, most MRE development has focused on utility-scale electrical grid generation, but a growing body of work focuses on non-grid applications in the blue economy where MRE could provide power on-site and at the scale needed for specific maritime sectors. One of the blue economy sectors with promising applications for MRE is ocean observations using both mobile and stationary platforms. This paper documents the steps and results of engaging with experts across the myriad ocean observation platforms and capabilities to inform five use cases. These use cases include descriptions of specific ocean observation applications performing measurements of high societal value (e.g., data for weather forecasting and tsunami detection) that closely resemble specific sensing systems and, in most cases, are placed in a particular area of the ocean. Rapid resource assessments (i.e., first-order estimates) were performed at these locations to determine the suitability of marine and other renewable energy sources. From the information gathered so far, MRE has significant potential to enable improved ocean observation missions, expand ocean observing capacity, and develop as an industry in parallel with the needs of our changing oceans. [ABSTRACT FROM AUTHOR]

An overview of the current European capacity in terms of operational modeling of marine and coastal systems is presented. This overview is compiled from a survey conducted in 2018–2019 among members of EuroGOOS and its related network of Regional Operational Oceanographic Systems, addressing the purposes, context and technical specificities of operational modeling systems. Contributions to the survey were received from 49 organizations around Europe, which represent 104 operational model systems simulating mostly hydrodynamics, biogeochemistry and sea waves. The analysis of contributions highlights the strengths and weaknesses of the current capacity from an operational point of view, and leads to the formulation of recommendations toward the improvement of marine operational modeling services in Europe. In particular, this study highlights the heterogeneity of the European operational modeling capacity in terms of atmospheric and land boundary conditions, its limited deployment for biogeochemical phenomena, and a restricted use of data assimilation methods. In order to improve the accuracy of their simulations, model operators aim toward a further refinement of spatial resolution, and identify the quality and accessibility of forcing data and the suitability of observations for data assimilation as restricting factors. The described issues call for institutional integration efforts and promotion of good practices to homogenize operational marine model implementations, and to ensure that external forcing datasets, observation networks and process formulations and parameterizations are adequately developed to enable the deployment of high-level operational marine and coastal modeling services across Europe.

Drowning accidents followed by the disappearance of the body are particularly distressing events. When such tragedy strikes, Search and Rescue Operations are usually deployed to recover the body. The efficiency of such efforts can be enhanced by timely data and appropriate data integration tools, such as operational prediction systems relying on numerical models or other data sources. In this paper, we propose four stages for Search and Rescue Operations after drowning accidents and briefly address the critical role of ocean observations at each stage, as well as the relevancy of available computational resources. The potential of the combination of different data sources on the state of the sea to provide better insights is discussed. This work encourages oceanographers, data scientists and relevant marine stakeholders to produce knowledge and tools to support Search and Rescue Operations after drowning accidents.

The Rockall Trough is one of the main conduits for warm Atlantic Water to the Nordic Seas. Ocean heat anomalies, originating from the eastern subpolar gyre, are known to influence Arctic sea ice extent, marine ecosystems, and continental climate. Knowledge of the transport through this basin has previously been limited to estimates from hydrographic sections which cannot characterize the intra‐annual and multiannual variability. As part of the Overturning in the Subpolar North Atlantic Programme (OSNAP), a mooring array was deployed in the Rockall Trough in order to obtain the first continuous measurements of transport. Here, we define the methodology and the errors associated with estimating these transports. Results show a 4‐year mean northward transport of 6.6 Sv (1 Sv = 106 m3/s) by the North Atlantic Current (NAC) in the east and interior of the Rockall Trough (2014–2018). A mean transport of −2.0 Sv (southward) is observed in the west of the basin, which could be part of a recirculation around the Rockall Plateau. The 90‐day low‐pass‐filtered transport shows large subannual and interannual variability (−1.6 to 9.1 Sv), mostly resulting from changes in the midbasin geostrophic transport. Satellite altimetry reveals the periods of low and high transport are associated with significant changes in the Rockall Trough circulation. There is a detectable seasonal signal, with the greatest transport in spring and autumn.Plain Language Summary: There is mounting evidence that the North Atlantic Current (eastward extension of the Gulf Stream) heavily influences the European and Arctic climate. To adequately measure this current and understand its dynamics, an array of underwater instruments was deployed in the Rockall Trough, a remote region of the eastern North Atlantic. Over a 4‐year period, these instruments continuously collected measurements of temperature, salinity, pressure, and velocity data. Analysis of these data provides a new and more accurate description of the North Atlantic Current in this region. This study reveals a surprisingly large variability in the eastern North Atlantic circulation. The combined analysis of underwater measurements and satellite data indicates that this variability is due to changes of the North Atlantic Current system.Key Points: For the first time, the strength of the North Atlantic Current (NAC) has been measured continuously for four years in the Rockall TroughDuring 2014 to 2018, about half the amount of warm water travelling northwards towards the Arctic Ocean flows through the Rockall TroughHigh northward transport periods are characterized by a strong NAC jet in the Rockall Trough, weak transport by mesoscale eddy activity [ABSTRACT FROM AUTHOR]

The relationship between age and oxygen is one that is often assumed in oceanography to be relatively simple. Because oxygen utilization rates are difficult to directly measure in the ocean, it is commonly assumed that the apparent oxygen utilization divided by the water age is a good representation of respiration. Likewise, because of limited transient tracer observations and difficulties constraining water age, it has been suggested that oxygen could be a useful proxy for age. In this paper, we explore the relationship between age and oxygen using observations from Line W, a repeat hydrography cruise track which crosses the Gulf Stream, extending from Cape Cod to Bermuda, and an Earth System Model simulation. In both the observations and the model, the assumed positive linear relationship between apparent oxygen utilization (AOU) and mean age is not found within and directly below the ventilated thermocline at the end of Line W. In the Earth System Model decoupling of age and AOU is found in gyre centers, in some coastal upwelling zones, and downstream of mode water formation regions that show large variability in isopycnal depth. In all three regions, differences in the spatial distribution of sources of age and AOU become critically important, producing offset maxima in the gyre centers, and different time variability of sources in the other two areas. [ABSTRACT FROM AUTHOR]

The operational Australian Bluelink ocean forecast system is used to transform physical oceanographic observations into coherent analyses and predictions. These analyses and predictions form the basis for information services about the marine environment and its ecosystem, and can provide boundary data for weather predictions. Bluelink information services are available to marine industries (e.g. commercial fishing, aquaculture, shipping, oil and gas, renewable energy), government agencies (e.g. search and rescue, defence, coastal management, environmental protection), and other stakeholders (e.g. recreation, water sports, artisanal and sport fishing) who depend on timely and accurate information about the marine environment. This review highlights the last 15 years of Bluelink achievements delivering mesoscale (eddy-resolving) to sub-mesoscale and short- to medium-range (days to weeks) ocean forecasts and reanalyses. Key achievements include the development of a global ocean forecasting and reanalysis system, a relocatable ocean-atmosphere model and a littoral zone analysis and forecasting capability. Beyond the traditional short-term forecasting of physical ocean properties (temperature, salinity, surface height, currents, waves), marine activities such as water quality and habitat management as well as climate monitoring increasingly rely on operational oceanographic data and products. These are areas of active research of the Bluelink team in collaboration with national and international partners. [ABSTRACT FROM AUTHOR]

Internal wave breaking upon sloping seafloors is a potential source of turbulent mixing in the deep-ocean, but we lack details on off-bottom breaking. Turbulence processes are relevant for the dispersal away from the seafloor of suspended materials like those emanating from thermal vents and artificial mining activities. For the present study, high-resolution temperature sensors have been moored up to 406 m above a slope of a 2000 m deep crest of the Mid-Atlantic Ridge. In addition to familiar observations of on-slope propagating highly nonlinear bores dominating turbulent mixing near and in contact with a sloping seafloor, the present observations show occasionally larger than 100 m tall turbulence expansions between 100 and 250 m above the seafloor at the transition from on- to off-slope flow. The details of such turbulence expansion are reminiscent of an asymmetric quasi-mode-2 internal hydraulic jump, with some specific differences compared with near-surface hydraulic jumps. As the expansion is generated at the transition from weak to steep edge of a saw-tooth internal tidal wave, it leads turbulence and stratification in two directions: One down to the seafloor in the direction of tidal phase propagation; the other more horizontally and slightly upward associated with near-homogeneous overturning remaining well away from the seafloor while preceding and sharpening near-bottom frontal bores. The mean turbulence dissipation rates O(10−8–10−7 m2s−3) associated with these expansions are half an order of magnitude less than those of on-slope propagating near-bottom bores, while about equal in duration. As for bores, their appearance, intensity and timing vary every tidal cycle. [ABSTRACT FROM AUTHOR]

In this paper, an innovative profiler driven by tidal energy for long-term oceanographic measurements in offshore areas with abundant tidal resources is investigated. The profiler is mainly composed of an oceanographic data collection system equipped with various sensors and a cross-plate that can make an upward or downward movement under the impact of tidal currents. Theoretical research is carried out through static analysis and numerical simulation, mainly studying the hydrodynamic characteristics of the cross-plate and its dynamic response to the current velocity. The theoretical model is verified by comparison with experiments. The research results show that tidal energy can be used as a kind of energy to drive the profiler’s ascent and descent motion and to continuously measure ocean parameters without using electric energy. The theoretical model established in this study can roughly predict the position of the profiler observation platform in the vertical direction under various current velocities. Furthermore, by studying the relationship between the current velocities and the lift and drag forces of the cross-plate in the fluid, it is recognized that the current velocity is an important factor affecting the stability of the system’s motion. It is hoped that this research will contribute to the development of profilers.

Following the global shutdown of tourism at the onset of the COVID-19 pandemic, small island developing states such as The Bahamas had their economies immobilized due to their heavy dependence on the industry. Beyond economic recovery in a post COVID-19 paradigm, the blue economy, blue growth, and associated activities offer pathways for a more resilient economy and is well-suited for The Bahamas. This paper suggests conduits for economic development using a traditional strength, coastal and marine tourism, in conjunction with the emerging fields of ocean renewable energy, offshore aquaculture, marine biotechnology, and bioprospecting. The interlinkages between each activity are discussed. Knowledge gaps in offshore aquaculture, ocean renewable energy, marine biotechnology, and marine environment monitoring are identified. In each sector case, strategic and tactical decision-making can be achieved through the exploitation of ocean numerical modeling and observations, and consequently should be invested in and developed alongside the requisite computational resources. Blue growth is encouraged, but instances of blue injustice are also highlighted. Crucially, pursuing blue economy activities should be given top national priority for economic recovery and prosperity.

Ocean acidification (OA) describes the progressive decrease in the pH of seawater and other cascading chemical changes resulting from oceanic uptake of atmospheric carbon. These changes can have important implications for marine ecosystems, creating risk for commercial industries, subsistence communities, cultural practices, and recreation. Characterizing the extent of acidification and predicting the ramifications for marine and freshwater resources and ecosystem services are critical to national and international climate mitigation discussions and to local communities that rely on these resources. Based on critical grassroots connections between scientists, stakeholders and decision makers, “Knowledge-to-Action” networks for ocean acidification issues have formed at local, regional and international scales to take action. Here, we review three examples of North American groups elevating the issue of ocean acidification at these three levels. They each focus on developing practicable, implementable steps to mitigate causes, to adapt to unavoidable change, and to build resilience to changing ocean conditions in the marine environment and coastal communities. While these first steps represent critical efforts in protecting ecosystems and economies from the risks posed by ocean acidification, some challenges remain. Sensitivity and risk to OA varies by region, species and ecosystems; priorities for action can vary between multiple and conflicting partners; evidence-based strategies for OA risk mitigation are still in the early stages; and gaps remain between scientific research and actionable decision-maker support products. However, the scaled networks profiled here have proven to be adept at identifying and addressing these barriers to action. In the future, it will be critical to expand funding for food web impact studies and development of decision support tools, and to maintain the connections between scientists and marine resource users to build resilience to ocean acidification impacts.

Sustained ocean observations provide an essential input to ocean scientific research. They also support a wide range of societal and economic benefits related to safety; operational efficiency; and regulation of activities around, on, in, and under seas and the ocean. The ocean economy is large and diverse, accounting for around US$1.5 trillion of global gross value-added economic activity. This is projected to more than double by 2030. Delivering this growth in economic activity is dependent on ocean observations. This review paper summarizes the projected changes in the scale and scope of the ocean economy and the role that observations, measurements, and forecasts play in supporting the safe and effective use of the ocean and ocean resources, at the same time as protecting the environment. It also provides an overview of key future work being planned to develop a better understanding of the present and likely future ocean economy and the role and value of ocean observations in its sustainable realization.

In 2004, the United Nations (UN) General Assembly approved a Regular Process to report on the environmental, economic and social aspects of the world’s ocean. The Regular Process for Global Reporting and Assessment of the State of the Marine Environment, including Socioeconomic Aspects produced the first global integrated assessment of the marine environment in December 2016 (known as the first World Ocean Assessment). The second assessment, to be delivered in December 2020, will build on the baselines included in the first assessment, with a focus on establishing trends in the marine environment with relevance to global reporting needs such as those associated with the UN Sustainable Development Goals. Central to the assessment process and its outputs are two components. First, is the utilization of ocean observation and monitoring outputs and research to temporally assess physical, chemical, biological, social, economic and cultural components of coastal and marine environments to establish their current state, impacts currently affecting coastal and marine environments, responses to those impacts and associated ongoing trends. Second, is the knowledge brokering of ocean observations and associated research to provide key information that can be utilized and applied to address management and policy needs at local, regional and global scales. Through identifying both knowledge gaps and capacity needs, the assessment process also provides direction to policy makers for the future development and deployment of sustained observation systems that are required for enhancing knowledge and supporting national aspirations associated with the sustainable development of coastal and marine ecosystems. Input from the ocean observation community, managers and policy makers is critical for ensuring that the vital information required for supporting the science policy interface objectives of the Regular Process is included in the assessment. This community white paper discusses developments in linking ocean observations and science with policy achieved as part of the assessment process, and those required for providing strategic linkages into the future.

In 1999, the consortium on Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and the satellite sea surface height measurements into a complete and coherent description of the ocean, afforded by an ocean general circulation model. Twenty years later, the versatility of ECCO's estimation framework enables the production of global and regional ocean and sea-ice state estimates, that incorporate not only the initial suite of data and its successors, but nearly all data streams available today. New observations include measurements from Argo floats, marine mammal-based hydrography, satellite retrievals of ocean bottom pressure and sea surface salinity, as well as ice-tethered profiled data in polar regions. The framework also produces improved estimates of uncertain inputs, including initial conditions, surface atmospheric state variables, and mixing parameters. The freely available state estimates and related efforts are property-conserving, allowing closed budget calculations that are a requisite to detect, quantify, and understand the evolution of climate-relevant signals, as mandated by the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The solutions can be reproduced by users through provision of the underlying modeling and assimilation machinery. Regional efforts have spun off that offer increased spatial resolution to better resolve relevant processes. Emerging foci of ECCO are on a global sea level changes, in particular contributions from polar ice sheets, and the increased use of biogeochemical and ecosystem data to constrain global cycles of carbon, nitrogen and oxygen. Challenges in the coming decade include provision of uncertainties, informing observing system design, globally increased resolution, and moving toward a coupled Earth system estimation with consistent momentum, heat and freshwater fluxes between the ocean, atmosphere, cryosphere and land.

Internal wave breaking upon sloping seafloors is a potential source of turbulent mixing in the deep-ocean, but we lack details on off-bottom breaking. Turbulence processes are relevant for the dispersal away from the seafloor of suspended materials like those emanating from thermal vents and artificial mining activities. For the present study, high-resolution temperature sensors have been moored up to 406 m above a slope of a 2000 m deep crest of the Mid-Atlantic Ridge. In addition to familiar observations of on-slope propagating highly nonlinear bores dominating turbulent mixing near and in contact with a sloping seafloor, the present observations show occasionally larger than 100 m tall turbulence expansions between 100 and 250 m above the seafloor at the transition from on- to off-slope flow. The details of such turbulence expansion are reminiscent of an asymmetric quasi-mode-2 internal hydraulic jump, with some specific differences compared with near-surface hydraulic jumps. As the expansion is generated at the transition from weak to steep edge of a saw-tooth internal tidal wave, it leads turbulence and stratification in two directions: One down to the seafloor in the direction of tidal phase propagation; the other more horizontally and slightly upward associated with near-homogeneous overturning remaining well away from the seafloor while preceding and sharpening near-bottom frontal bores. The mean turbulence dissipation rates O(10−8–10−7 m2s−3) associated with these expansions are half an order of magnitude less than those of on-slope propagating near-bottom bores, while about equal in duration. As for bores, their appearance, intensity and timing vary every tidal cycle.

Current ocean wave observation is achieved by separate battery-powered sensing and signal transmission modules. Owing to the limited electrical supply and information channel space, the long-time span observation is restricted and only wave height and period information rather than the whole wave profile are sent back to the receiver. In this work, a self-powered ocean wave observation system was achieved by a developed polymer network liquid crystal (PNLC)-based smart reflector powered by a tailored triboelectric nanogenerator embedded with one-way overrunning clutches. The off-shore smart reflector modulated the on-shore emitted laser light, where ocean wave motion information can be revealed from the remotely detected reflected laser light without cable connections. The ocean wave rise and fall are distinguished by the developed one-way overrunning clutch, which selects the TENG to power the PNLC. Through the developed paradigm, ocean wave sensing and signal transmission can be achieved simultaneously, which is fully self-powered and free-of-cable. The flume-based self-powered ocean observation was performed with demonstrated wave height and period sensing accuracies of 92.66 and 97.32%, respectively.