Coastal seas and estuaries are among the most productive ecosystems on Earth and have long attracted human activity. Yet, urbanization pressures are intense and are compounded by accelerating climate stresses. Urban seas are now hotspots of stress in the Anthropocene ocean. The Salish Sea stands out as one of a few highly functioning urban seas in the world, boasting ecological riches and thriving coastal communities and industries, including tourism. For over 10,000 years the region has supported Indigenous peoples; now it is home to a growing population of almost nine million people, concentrated in and near the major cities of Seattle, Washington, and Vancouver, British Columbia. Increasing urbanization combined with intensifying climate stress is degrading the Salish Sea and acutely affecting communities already experiencing marginalization. Current environmental impacts include acidifying waters, hypoxia, and intense heat waves, all of which have had measurable impacts within the ecosystem. A recent synthesis of this system identified key domains for solutions, which we generalize here for invoking positive change in global urban seas: 1) innovation in data collection, curation, and integration using a systems approach in science and management; 2) sharing place-based knowledge to sustain community-based action; and 3) aligning science and policy with ecosystem boundaries. The differing governance and socio-political settings across two countries and numerous Indigenous nations creates a complex challenge in ecosystem management. Developing actionable solutions for people and the biota of the Salish Sea can create a global example of a sustainably managed urban sea with transferable insights to other urban seas in need of revitalization around the world.

Abstract Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from >20 years of investigations to demonstrate the nature of fluid‐flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near‐seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite‐to‐seafloor reflection polarity, and are associated with frequency reduction and velocity push‐down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high‐amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom‐video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios <500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate‐related bottom‐simulating reflectors are widespread and occur at depths indicating heat flow values of 80–90 mW/m2.

Abstract The 2015 eruption at Axial Seamount, an active volcano at a depth of 1500 m in the Northeast Pacific, marked the first time a seafloor eruption was detected and monitored by an in situ cabled observatory—the Cabled Array, which is part of the Ocean Observatories Initiative. After the onset of the eruption, eight cabled and noncabled instruments on the seafloor recorded unusual, nearly synchronous and spatially uniform temperature increases of 0.6–0.7°C across the southern half of the caldera and neighboring areas. These temperature signals were substantially different from those observed after the 2011 and 1998 eruptions at Axial and hence cannot be explained by emplacement of the 2015 lava flows on the seafloor. In this study, we investigate several possible explanations for the 2015 temperature anomalies and use a numerical model to test our preferred hypothesis that the temperature increases were caused by the release of a warm, dense brine that had previously been stored in the crust. If our interpretation is correct, this is the first time that the release of a hydrothermal brine has been observed due to a submarine eruption. This observation would have important implications for the salt balance of hydrothermal systems and the fate of brines stored in the subsurface. The observation of the 2015 temperature anomalies and the modeling presented in this study also demonstrate the importance of contemporaneous water column observations to better understand hydrothermal impacts of submarine eruptions.

Long-term, persistent Resident AUV (RAUV) systems, able to be deployed for months to years without manned support vessels, will have a profound impact on our ability to observe temporally and spatially changing phenomena throughout entire volumes of the ocean. Further, RAUVs may provide a means of remotely interacting with subsea infrastructure, offering tremendous savings on maintenance that would otherwise require manned vessels and ROVs.During a workshop in May, 2018, 100 participants gathered in Seattle, WA to assess opportunities for RAUVs. Applications evaluated range from observing mid-ocean ridge volcanic eruptions, to intermittent methane seep activity, to arctic ice motion, and eventually to the search for life in off-planet oceans. In all cases, long-term RAUV deployments will require a system of components for energy management, communications, navigation, as well as self-diagnostics and advanced autonomy functions. While many of the subsystems necessary for viable residency have been demonstrated individually, it will take time, testing and focused system and reliability engineering before RAUV operations become routine. As evidenced by the spectrum of industry and academic participants in the workshop, industry-academic partnerships may be a plausible means of accelerating RAUV systems and applications.

Gas hydrate deposits along continental margins are commonly associated with overlying methane seeps, which support extensive biological communities on and within the sediments. In addition, the rising methane-rich plumes may be responsible for increased biological productivity within the overlying ocean. The extent to which methane seeps contribute to oceanic and atmospheric carbon is thought to be relatively minor, but this conclusion is largely based on infrequent observations of bubble release over short timescales. Here, we present initial results of bubble plume variability from a cabled Acoustic Doppler Current Profiler (ADCP) deployed for 2 years at Southern Hydrate Ridge (SHR), a well-studied hydrate-bearing seep site off the coast of Oregon. This area is characterized by extensive bacterial mats, focused venting of bubble plumes, and rare exposed gas hydrate on the seafloor. The upward-looking ADCP is a part of NSF's Ocean Observatories Initiatives Cabled Array infrastructure at SHR. Live data from eleven cabled instruments and three un-cabled sensors at SHR for which data are collected post annual Operations and Maintenance cruise enable long-term monitoring of process linkages at SHR seeps. Preliminary results indicate that bubble plumes extend over much of the water column at SHR, though further analysis is required to determine whether seepage is forced over tidal periods. Future studies involving the incorporation of data from proximal instrumentation at SHR would provide a comprehensive understanding of the link between subsurface gas transport and gas distribution throughout the overlying water column

Every few hundred years, the Cascadia subduction zone off the coast of the Pacific Northwest hosts devastating earthquakes, and there is a growing awareness of the need to be prepared for these events. An offshore cabled observatory extending the length of the Cascadia subduction zone would enhance the performance of the earthquake and tsunami early warning systems, would enable real time monitoring and predictions of the incoming tsunami, and would contribute substantially to scientific research aimed at mitigating the hazard. The University of Washington has recently initiated a study to develop a conceptual design for the U.S. portion of an offshore observatory for earthquake and tsunami early warning and research. This paper presents the motivation for this work and plans for the study.

The Ocean Observatories Initiative Cabled Array has provided an unprecedented real-time window on the dynamics of Axial Volcano since fall 2014. In April and May of 2015, for the first time, researchers on shore were able to monitor an eruption event as it happened. The seismic, deformation and acoustic signals sent to shore were analyzed to determine the precise locations of diking events, followed hours later by acoustic impulses corresponding to lava expulsion from the seafloor. Although these locations informed follow-up Autonomous Underwater Vehicle (AUV) mapping expeditions which produced high resolution bathymetry, to date, the evolution of an eruptive event and its immediate impact on the surrounding ecosystem have not been observed. Although the 70,000 km-long mid ocean ridge (MOR) must generate many hundreds of powerful, transient events every year, they have never been characterized as they form. We envision a Resident AUV with in situ charging and data download capabilities, shore-based mission control, and an array of bottom-mounted acoustic positioning beacons that can concurrently be used as a multi-hop sensor network. This system will provide unprecedented observing capabilities before, during, and after the next eruption and formation of the highly energetic eruptive (mega) plume. AUV capabilities will include high-resolution bathymetry, high definition video and still imagery, and 3-D water chemistry and microbial sampling throughout the water column, while the acoustic array will monitor horizontal and vertical deformation.

The most scientifically diverse and technologically advanced component of the National Science Foundations' $386M investment in the Ocean Observatories Initiative (OOI), involves 900 kilometers of high power and bandwidth electro-optical cable extending from Pacific City, OR, across active portions of the Juan de Fuca tectonic plate and up into the overlying ocean. Completed on time and under budget in October, 2014, this mesoscale fiber-optic sensor array enables real-time, high-bandwidth, 2-way communication with seafloor and water-column sensor networks across: 1) a portion of the global Mid-Ocean Ridge (MOR), 2) a section of the Cascadia Subduction Zone, and, 3) a cross-section of the California Current, a component of the North Pacific Gyre. Much of the data generated from >130 fiber-linked instruments has become available for scientific, educational and public user communities over the past 6 to 12 months, via the OOI Cyber-infrastructure (http://oceanobservatories.org/data-portal/). Since the OOI Cabled System has been in use and streaming live data to shore, two major developments have emerged that bear on undersea volcano-hydrothermal systems: 1) The 2015 submarine eruption of Axial Seamount was documented in a unique fashion by 20 remote, hardwired instruments distributed across the floor of the summit caldera. 2) Live, streaming video of an active hydrothermal system within one of the vent fields inside the caldera reveals subtle changes taking place in the Axial system.

In 2015, the Cabled Array became operational streaming real-time data to shore from a diverse array of 140 instruments. The network spans the Juan de Fuca tectonic plate, with two cables extending from a Shore Station in Pacific City, Oregon. One branch extends ~480 km due west to Axial Seamount, the largest volcano on the Juan de Fuca Ridge. The second branch extends 208 km southward along the base of the Cascadia Subduction Zone (2900 m) and then turns east extending 147 km to 80 m water depth offshore Newport, Oregon. The system is designed for a 25-year lifetime. The Cabled Array includes six state-of-the-art instrumented, full water column moorings (up to 2900 m water depth) hosting instrumented wire crawlers, winched science pods, and platforms to study linkages among physical, biological and chemical processes spanning blue water to coastal systems along the Cascadia Margin. The coastal array is located at highly productive coastal sites strongly impacted by the California Current, upwelling, ocean acidification, and hypoxia events. The network also includes cutting edge seafloor sensors focused on understanding active volcanism, life in extreme environments, seismicity, and biogeochemical processes and fluxes in actively forming gas hydrate systems. Two-way 24/7/365 communication with direct connection to the Internet, with expansion up to 240 Gb/s and high power (8 kW), allow highly interactive, rapid responses with adaptive sampling to events such as formation of thin layers, large storms, internal waves, volcanic eruptions, and earthquakes. With an operational life of at least 25 years, the Cabled Array will provide decades of sustained, high quality coregistered, multidisciplinary data at rates up to 250 kilisamples/second and at spatial resolutions of centimeters to kilometers. The high bandwidth and power provides significant expansion capabilities for innovative sensing systems that include advancement of autonomous vehicles with companion docking stations that can change missions in response to changing conditions without human intervention, 3D imagers, and in situ DNA samplers. International installation of progressively advanced submarine cabled observatories will provide unprecedented monitoring of the oceans, and the entrainment of a global community of users - researchers, educators, policy makers and the public.

Abstract In Oct, 2014, installation of the largest North American scientific cabled observatory was completed. The Cabled Array portion of the Ocean Observatories Initiative, funded by the U.S. National Science Foundation and implemented by the University of Washington, consists of over 850 km of fiber optic and electrical cables, 7 primary nodes, 18 seafloor junction boxes, 3 mooring-mounted winched profiling systems, 3 rechargeable wire-crawling profiler systems and 140 science instruments. The primary nodes and backbone cables, installed using standard telecommunications industry practices and designed to last a quarter century, bring unprecedented power and bandwidth to remote seafloor locations. Meanwhile, the modular, ROV-serviceable secondary infrastructure branches power and communications in support of instrumentation throughout the water column. The modular design of the secondary infrastructure provides the capacity to expand the cabled network well beyond its initial footprint. To facilitate full shore-based operations, a suite of management software was developed for network configuration, power control, port monitoring, system condition monitoring, configuring alarms, and troubleshooting. These systems are part of a growing new trend of real-time remote ocean monitoring, or interactive observatory-class, systems. The purpose-built observatory-class systems for the OOI Cabled Array's long-term sub-sea monitoring operations provide a modular framework capable of adapting to many applications and scales. All secondary infrastructure equipment, including cables up to 5 km, were deployed by a work class ROV and configured to fit multiple site geometries and environments, from soft sediments to volcanic crust. Seafloor nodes, or junction boxes, deliver up to 200 Watts to each of 8 instrument ports, and can be daisy-chained for expansion. Real-time controllable winched profilers routinely perform multiple 200 m vertical profiles daily, and can be docked as needed to accommodate operations in the water column above. A 3500-meter rated wire-crawling profiler samples the entire water column and recharges at a cabled seafloor docking station. While each system is tailored to its specific mission, all components of the secondary infrastructure: 1) enable remote shore-based operation of deployed equipment, 2) allow for real or near-real time data collection and system control, and 3) are synchronized to a GPS-based clock. These key attributes of interactive observatory-class systems unlock several possibilities for subsea systems, including immediate responses to detected events, accurate time-based comparisons of spatially-varying data sets, synchronized operations over an extended area, and shore-based control of remote resident infrastructure.