An Enhanced Ocean Acidification Observing Network: From People to Technology to Data Synthesis and Information Exchange

POLICY AND PRACTICE REVIEWS published: 19 June 2019 doi: 10.3389/fmars.2019.00337 Edited by: Frank Edgar Muller-Karger, University of South Florida, United States Reviewed by: Scott Doney, University of Virginia, United States Philip Bresnahan, University of California, San Diego, United States *Correspondence: Bronte Tilbrook [email protected] Specialty section: This article was submitted to Ocean Observation, a section of the journal Frontiers in Marine Science Received: 09 November 2018 Accepted: 03 June 2019 Published: 19 June 2019 Citation: Tilbrook B, Jewett EB, DeGrandpre MD, Hernandez-Ayon JM, Feely RA, Gledhill DK, Hansson L, Isensee K, Kurz ML, Newton JA, Siedlecki SA, Chai F, Dupont S, Graco M, Calvo E, Greeley D, Kapsenberg L, Lebrec M, Pelejero C, Schoo KL and Telszewski M (2019) An Enhanced Ocean Acidification Observing Network: From People to Technology to Data Synthesis and Information Exchange. Front. Mar. Sci. 6:337. doi: 10.3389/fmars.2019.00337 An Enhanced Ocean Acidification Observing Network: From People to Technology to Data Synthesis and Information Exchange Bronte Tilbrook1,2*, Elizabeth B. Jewett3, Michael D. DeGrandpre4, Jose Martin Hernandez-Ayon5, Richard A. Feely6, Dwight K. Gledhill3, Lina Hansson7, Kirsten Isensee8, Meredith L. Kurz3, Janet A. Newton9, Samantha A. Siedlecki10, Fei Chai11,12, Sam Dupont13, Michelle Graco14, Eva Calvo15, Dana Greeley6, Lydia Kapsenberg15, Marine Lebrec7, Carles Pelejero15,16, Katherina L. Schoo8and Maciej Telszewski17 1Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Hobart, TAS, Australia, 2Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, TAS, Australia, 3Ocean Acidification Program, National Oceanic and Atmospheric Administration, Silver Spring, MD, United States, 4Department of Chemistry and Biochemistry, University of Montana, Missoula, MT, United States, 5Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Ensenada, Mexico, 6Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, WA, United States, 7Ocean Acidification International Coordination Centre, International Atomic Energy Agency Environment Laboratories, Monaco, Monaco, 8Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific and Cultural Organization, Paris, France, 9Applied Physics Laboratory and College of the Environment, University of Washington, Seattle, WA, United States, 10 Department of Marine Sciences, University of Connecticut, Groton, CT, United States, 11 State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China, 12 School of Marine Sciences, University of Maine, Orono, ME, United States, 13 Department of Biological and Environmental Sciences, University of Gothenburg, Kristineberg, Sweden, 14 Instituto del Mar del Perú, Lima, Peru, 15 Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, Barcelona, Spain, 16 Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain, 17 Institute of Oceanology of the Polish Academy of Sciences, Sopot, Poland A successful integrated ocean acidification (OA) observing network must include (1) scientists and technicians from a range of disciplines from physics to chemistry to biology to technology development; (2) government, private, and intergovernmental support; (3) regional cohorts working together on regionally specific issues; (4) publicly accessible data from the open ocean to coastal to estuarine systems; (5) close integration with other networks focusing on related measurements or issues including the social and economic consequences of OA; and (6) observation-based informational products useful for decision making such as management of fisheries and aquaculture. The Global Ocean Acidification Observing Network (GOA-ON), a key player in this vision, seeks to expand and enhance geographic extent and availability of coastal and open ocean observing data to ultimately inform adaptive measures and policy action, especially in support of the United Nations 2030 Agenda for Sustainable Development. GOA-ON works to empower and support regional collaborative networks such as the Latin American Ocean Acidification Network, supports new scientists entering the field with training, mentorship, and equipment, refines approaches for tracking biological impacts, and stimulates development of lower-cost methodology and technologies Frontiers in Marine Science | www.frontiersin.org 1June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network allowing for wider participation of scientists. GOA-ON seeks to collaborate with and complement work done by other observing networks such as those focused on carbon flux into the ocean, tracking of carbon and oxygen in the ocean, observing biological diversity, and determining shortand long-term variability in these and other ocean parameters through space and time. Keywords: Global Ocean Acidification Observing Network, Sustainable Development Goal, ocean acidification, ecosystem stressors, capacity building INTRODUCTION The ocean has absorbed approximately 30% of anthropogenic carbon dioxide (CO2) emissions since the industrial era began (Intergovernmental Panel on Climate Change (IPCC), 2013). Ocean acidification (OA), or the ongoing observed increase in marine acidity, is a direct result of this uptake (Doney et al., 2009; Intergovernmental Panel on Climate Change (IPCC), 2013). The average surface ocean pH has decreased by approximately 0.11 units from a preindustrial mean value of 8.17, this represents an increase of about 28% in hydrogen ion concentration (Intergovernmental Panel on Climate Change (IPCC), 2013). By the end of this century, surface ocean pH is expected to decline by another 0.1–0.4 units, and carbonate ion (CO32−) concentration is expected to decline by as much as 50% over the same period compared to preindustrial conditions (Feely et al., 2004;Orr et al., 2005;Doney et al., 2009;Gattuso et al., 2015). Ocean acidification has the potential to impact marine organisms in a variety of ways, including effects from decreased pH, elevated partial pressure of CO2(pCO2), and decreases in the calcium carbonate (CaCO3) saturation state. Changes in the CaCO3saturation state (Feely et al., 2004) make conditions corrosive for many calcifying organisms such as many species of molluscs, corals, echinoderms, and calcifying plankton, with potential dissolution of calcareous structures such as shells or skeletons (Eyre et al., 2018;Harvey et al., 2018). Changing carbonate chemistry also impacts the process of calcification in many species (Kroecker et al., 2013;Albright et al., 2016; Bednaršek et al., 2017). Less direct impacts can occur where declines in calcification of key habitat forming organisms result in ecosystem shifts and loss of the structural complexity and biodiversity of coral reefs and other benthic communities (Fabricius et al., 2014;Sunday et al., 2016). Negative impacts of changing ocean carbonate chemistry have already been observed in calcifying organisms living in some regions of coastal upwelling where natural acidity is relatively high (Bednaršek et al., 2014, 2017). Research also suggests that changing ocean chemistry and reduced pH may affect the physiology, behavior, and population dynamics of many non-calcifying species (Doney et al., 2009;Gattuso et al., 2015). Over the past decade, the OA research community has grown rapidly, and the number of publications related to OA has grown exponentially (Figures 1,2). In the context of this burgeoning growth, the ocean observing community recognized a need for global coordination at OceanObs’09 (Feely et al., 2010) and has since made progress on collaborative efforts. The potential impacts to marine ecosystems have resulted in OA becoming one of only ten targets for the United Nations (UN) Sustainable Development Goal (SDG) 14 on the conservation and sustainable use of marine resources. The World Meteorological Organization has also included OA as a headline climate indicator, recognizing the link to increasing atmospheric carbon dioxide concentrations and the climate system. The challenges facing OA researchers, current and future coordinating activities, and a vision in light of the upcoming United Nations Decade of Ocean Science for Sustainable Development (2021–2030) for future OA observing are discussed in this white paper. CHALLENGE The adaptive capacity of organisms that may be impacted by changing ocean chemistry is not well known, and a great deal of work must be done to understand the interactions of multiple stressors and their potential ramifications for marine ecosystems and the human communities that depend on their health. Further, while OA due to an increased atmospheric CO2 concentration occurs in all marine waters, carbonate chemistry in coastal waters is affected by additional processes, such as nutrient addition and its effect on respiration, meaning that coastal acidification may be driven by more factors than just the increase in atmospheric CO2. The longest time-series observing assets to date have been deployed within several open-ocean environments where they have documented surface water pCO2values mostly tracking the long-term trend in rising atmospheric CO2(Figure 3), demonstrating that the global ocean carbon storage has increased since 2000 (Blunden et al., 2018;Feely et al., 2018;Le Quéré et al., 2018). Recent observations within shelf waters have been shown in some regions to lag atmospheric CO2, indicating a tendency for enhanced shelf uptake of atmospheric CO2from the aqueous phase into biomass (Laruelle et al., 2018). Other coastal regions exhibit more rapid increases in pCO2relative to the open ocean, indicating more rapid acidification due to the additive effects of CO2uptake and increased upwelling (Chavez et al., 2017). Coastal seas have been suggested to have changed in the recent past from a net source to a net sink (Bauer et al., 2013;Fennel et al., 2018;Laruelle et al., 2018). The enhanced uptake of CO2by the ocean and shelves also changes the rate at which waters acidify, altering local rates of acidification, a process not well simulated by coarse global simulation models nor adequately captured by many direct measurements from the existing observing system. The local processes that govern these modifications may also serve to amplify (or dampen) global Frontiers in Marine Science | www.frontiersin.org 2June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network FIGURE 1 | Annual number of peer-reviewed publications on ocean acidification and number of authors involved during the period 1900–2018. Figure produced by Jean-Pierre Gattuso using the bibliographic database of the IAEA Ocean Acidification International Coordination Centre (OA-ICC). FIGURE 2 | Global distribution of ocean acidification publications by country, based on first author affiliation. Data from the IAEA Ocean Acidification International Coordination Centre (OA-ICC). changes expected from global earth system model projections, potentially altering the ecological consequences for shelf systems. In addition to variability in time, the rates of uptake of CO2from the atmosphere also vary spatially, especially in coastal and shelf seas (Fennel et al., 2018;Laruelle et al., 2018). The magnitude of the sink of carbon has been shown to vary latitudinally, with high latitude (north of 30◦) coastal seas providing a sink while low latitude shelves are generally a source or neutral (Cai et al., 2006;Bauer et al., 2013;Chen et al., 2013). Spatial and temporal variability poses a challenge to the observational and modeling communities that could be better addressed with new tools and sensors, capabilities and technologies (see Next Generation Sensor Technologies to Enhance the Observing System), and through international collaborative efforts like GOA-ON. The scientific challenges that the coastal variability imparts on stakeholders, managers, coastal communities, and other marine resource end-users poses unique challenges for attribution science, habitat shift projections, and stress response timing for vulnerable ecosystems. Below we describe some of the new tools, capabilities, and technologies available to be ported through new informational products served through GOA-ON, as well as the empowerment this global network offers coastal communities. NETWORK GENESIS AND CONTEXT Ocean observation, monitoring systems, and networks are designed to quantify variability and long-term changes, and to discover natural dynamics and anthropogenic impacts. The Frontiers in Marine Science | www.frontiersin.org 3June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network FIGURE 3 | Time series of in situ pCO2(top) and pHT(bottom) for three time series stations in the Atlantic and Pacific Oceans. Data sources: BATS data: http://batsftp.bios.edu/BATS/bottle/; Hot data: University of Hawaii (http://hahana.soest.hawaii.edu/hot/products/HOT_surface_CO2; ESTOC data: https://www.nodc.noaa.gov/archive/arc0051/0100064/1.1/data/0-data/). Global Ocean Observing System (GOOS), now considered the core, community-vetted ocean observing system for guidance, utilizes the Framework for Ocean Observing to implement an integrated and sustained ocean observing system (Intergovernmental Oceanographic Commission (IOC)- UNESCO, 2012). This systems approach is designed to be flexible and to adapt to evolving scientific, technological, and societal needs, helping to deliver an ocean observing system tailored to user needs and the mitigation of societal impact. Within this framework, OA is included as one phenomenon for inorganic carbon in the Essential Ocean Variables (EOV) suite1. The genesis of a global OA observing network with a multidisciplinary focus can be traced to an internationally authored OceanObs’09 community white paper, An International Observational Network for Ocean Acidification (Feely et al., 2010). This paper recommended “an integrated international interdisciplinary program of ship-based hydrography, time-series moorings, floats and gliders with carbon system, pH and oxygen sensors, and ecological surveys to determine the large-scale changes in the properties of ocean water and the associated biological responses to OA.” Following panel discussions at OceanObs’09, the groundswell of scientists interested in this effort increased and broadened in discipline and expertise. In 2012, a workshop was held in Seattle, WA, United States, to design a global OA observing network that would delineate the physical–chemical processes controlling the acidification of the oceans and their large-scale biological impacts and was aligned with the EOV process. Workshop participants defined the goals and requirements of a global OA observing network in the context of responding to societal needs. Outcomes of the Seattle meeting were community definition of the rationale, goals, design, suite of measurement parameters, 1GOOS EOV Suite: http://www.goosocean.org/components/com_oe/oe.php? task=download&id=35906&version=2.0&lang=1&format=1. data quality objectives, data distribution strategies, and integration with international programs (Newton et al., 2013). The rationale and design of the components and locations considered existing networks and programs and identified gaps in both open-ocean and coastal regions. The minimum suite of measurement parameters and performance metrics identified two different usage cases with the data quality objectives needed to support these: (1) “Climate” is defined as measurements of quality sufficient to assess long-term trends with a defined level of confidence. With respect to OA, climate-quality data support detection of the long-term anthropogenically driven changes in hydrographic conditions and carbon chemistry over multidecadal timescales. (2) “Weather” is defined as measurements of quality sufficient to identify relative spatial patterns and short-term variation, particularly in nearshore regions where variability is higher (Table 1). Weather-quality data support mechanistic interpretation of the ecosystem response to OA and understanding of local, immediate OA dynamics. The name, Global Ocean Acidification Observing Network (GOA-ON), was coined at the workshop2. GOA-ON serves three goals to (1) improve understanding of global OA conditions; (2) improve understanding of ecosystem response to OA; and (3) acquire and exchange data and knowledge necessary to optimize modeling of OA and its impacts (Newton et al., 2015). Thus, GOA-ON focuses on both chemistry and biology, and through its data portal3, it provides discoverability of—and in some cases access to—data for myriad uses, including to improve forecast modeling and prediction of the future ocean. The GOA-ON community held a second workshop in St. Andrews, United Kingdom, in 2013 to refine the vision for the structure of GOA-ON, with emphasis on defining monitoring 2GOA-ON website: https://www.goa-on.org. 3http://portal.goa-on.org/Explorer Frontiers in Marine Science | www.frontiersin.org 4June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network TABLE 1 | Recommended measurement uncertainties for climate and weather from Newton et al. (2015). Parameter Climate Uncertainty Weather Uncertainty TCO22µmol/kg 10 µmol/kg TA 2 µmol/kg 10 µmol/kg pCO22µatm 10 µatm pH 0.003 0.02 Aragonite Saturation 0.04 0.2 Calcite Saturation 0.06 0.3 for ecosystem impacts of OA in shelf and coastal seas (Newton et al., 2013). After this workshop, the development of a data portal commenced to provide OA-relevant asset locations and metadata, with a vision toward serving data products. The portal was made possible through an initial investment by the University of Washington and by leveraging existing capacity funded by the United States Integrated Ocean Observing System (U.S. IOOS). GOA-ON reached out to its members to populate the data portal, housed at the GOA-ON website, with their observing information. At a third workshop in Hobart, Australia, in 2016, major outcomes were related to the building and reinforcement of communities to increase regional coordination, with identification of regional implementation needs, including information, data products, and capacity building. The GOA-ON mentorship program known as “Pier2Peer” (described below) was launched at this workshop. Regional OA networks, acting as regional hubs of GOA-ON, have emerged in Latin America, Africa, the Western Pacific, Europe, the South Pacific Islands, and North America. Advances have been made in capacity building, and the GOA-ON community has expanded to more than 600 members from 94 countries as of March 2019 (Figure 4). A fourth workshop in April 2019 in Hangzhou, China, targeted further development of a coordinated network and regional engagement. Workshop themes covered were ocean and coastal acidification in a multi-stressor environment; observing ocean and coastal acidification and impacts on ecosystems; modeling and forecasting ocean and coastal acidification and ecosystem responses; and focusing GOA-ON efforts for societal benefit, stakeholder needs, and capacity building. The vision for the future of the global OA observing network, described in this white paper, is built around eight components: (1) Optimize GOA-ON to better inform modeling community needs; (2) Fill gaps in understanding of chemical changes and biological impacts; (3) Promote and advise the development of next generation sensor technology; (4) Support the growth of regional hubs and grassroots establishment of new hubs; (5) Expand and enhance capacity-building efforts to enable broader participation; (6) Improve the GOA-ON data portal; (7) Build OA networks producing scientific data and information designed to inform regional and international environmental action; and (8) Enhance collaboration with other observing networks. GOA-ON REQUIREMENTS AND GOVERNANCE Ocean acidification is a global issue, but it has local effects that differ depending on the environment (e.g., sensitivity of local species), and societal uses of the ocean and its resources. An approach that coordinates effort, so that global as well as local status could be assessed effectively and with consistent methods, was deemed necessary during the initial workshops held by GOAON. The OA data quality definition of Climate and Weather, based on data application, was an important step for GOA-ON. Many international or local climate assessments require climate quality data both in the open ocean and coastal seas (Karl et al., 2010). The inherent variability in coastal areas results in more FIGURE 4 | Countries with GOA-ON members as of April 2019 are shaded black, excluding representatives of UN bodies. Frontiers in Marine Science | www.frontiersin.org 5June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network years of climate-quality data being required to observe trends (Sutton et al., 2018) compared to the open ocean. Uses such as monitoring for aquaculture and biological experiments, or for interpretations of local mechanisms underlying temporal and spatial variation can be served by either weather-quality data or climate-quality data. Three levels of measurements were defined for the two observational goals, with level 1 being critical measurements, level 2 enhanced measurements that allow further understanding, and level 3 those in development or experimental measurements. In general, it was much easier for the community to define requirements for goal 1, OA status, than for goal 2, ecosystem response. For the latter, the participants considered diverse environments, such as polar, temperate, tropical, nearshore, and coral habitats. Goal 1 level 1 variables are: temperature, salinity, oxygen, depth, and carbon-system constraints. Carbon-system constraints are achievable in a number of ways, including combinations of direct measurements and estimates based on measurements of at least two carbon-system variables. Two further variables, fluorescence and irradiance, were considered important, except where the platform is not appropriate or available for such measurements. Goal 2 variables provide additional detail, and the “level” requirements are defined by usage. In general, these include the goal 1 variables named above, plus variables describing phytoplankton, zooplankton, benthic producers and consumers in shelf seas and nearshore, nutrients, organic carbon and nitrogen, and microbial measures. The outcome from the GOA-ON vision and plan is to enable globally accessible high-quality data and data synthesis products that facilitate research and new knowledge on OA, communicate the status of OA and biological response, and enable forecasting of OA conditions. End-uses of these data include support for the development of national and international policy and adaptive action, including those related to carbon emission policies, food security and livelihoods, fisheries and shellfish aquaculture practices, protection of coral reefs, shore protection, cultural identity, and tourism. However, investment in capacity in multiple areas critical to meet these needs must be addressed, including physical observing infrastructure, operations and maintenance, data QA/QC, analytical and synthesis activities, and the intellectual infrastructure. Since the launch of the Global Ocean Acidification Observing Network in 2013, forward momentum has been maintained by an Executive Council of experts from around the world who either represent core scientific disciplines or international or national institutions with a leadership role in the network. A distributed secretariat was established in 2018 with support from the International Atomic Energy Agency, the Intergovernmental Oceanographic Commission, and the U.S. National Oceanic and Atmospheric Administration (NOAA) Ocean Acidification Program. The secretariat has a key role in the development of GOA-ON through the coordination and communication of activities and in building science-policy linkages. The data portal and website services are also part of the distributed secretariat, supported by NOAA’s Ocean Acidification Program, U.S. IOOS, and the University of Washington. STATUS OF THE OBSERVING NETWORK The observing network cataloged and guided by GOA-ON represents a multinational coordination effort to harmonize ocean observing strategies aimed toward acquiring robust evidence on OA and its worldwide impacts, guiding management action from regional to international levels, and informing policy decisions. Participating scientists adhere closely to the established observing requirements detailed in the GOA-ON Requirements and Governance document (Newton et al., 2015), which is oriented around the three goals outlined in Section “Network Genesis and Context” of this paper. In accordance with these requirements, the existing observing network is composed of assets deployed across multiple ecosystem domains ranging from large-scale open-ocean regions to coastal environments inclusive of large estuaries and embayments. Assets deployed by GOA-ON participants are located in ecosystems as divergent as the Arctic pelagic seas to tropical coral reefs and use of a broad range of asset types from ship-based sampling to diver collection teams. Perhaps the most unique aspect of the GOA-ON observing network is the emphasis on interdisciplinary observations including carbon chemistry, meteorology, oceanography, biogeochemistry, ecology, and biology. The goal is not only to track OA, but also to understand and monitor the ecological changes that may result, and this sets GOA-ON apart from many other observing systems. One example of this transdisciplinary approach is the strategy employed in coral reef monitoring. NOAA established a coordinated national coral reef monitoring strategy that includes a broad suite of OA-relevant ecological metrics, including the adoption of standardized Calcium Carbonate Accretion (CCA) and bioerosion indices, which are deployed in tandem with regular carbonate chemistry monitoring (pCO2sea, pCO2air, and pH) together with temperature, salinity, oxygen, fluorescence, and turbidity. The protocols and methods adopted by NOAA for coral reef OA monitoring have since been shared with the international community through a series of workshops that have fostered the adoption of similar methods throughout Western Pacific nations and elsewhere. The current GOA-ON observing network4is composed of 598 assets deployed around the world and supported by 54 nations. The assets include 247 ship-based time series, 151 moorings, 118 fixed ocean time series, 30 repeat hydrography lines, and 22 volunteer observing ships (Figure 5). However, only about two thirds of the reported assets include dual measures of the carbonate system, which is a necessary minimum prerequisite for fully constraining the system as called for under the GOA-ON requirements. Only about 30% of the assets on the portal have associated links to open-access data. Many of the assets are deployed in specific open-ocean locations and along coastal and shelf margins that are likely to be heavily impacted by coastal biogeochemical processes. This makes direct detection of OA more challenging, particularly in the absence of suitable regionally scaled biogeochemical models that can be used for ascribing the specific drivers behind 4http://portal.goa-on.org/Explorer Frontiers in Marine Science | www.frontiersin.org 6June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network FIGURE 5 | Present-day (as of April 2019) Global Ocean Acidification Observing Network which is collaborative with the GO-SHIP, Ocean SITES, SOCONET, SOOP communities and other open-ocean and coastal observing networks. the observed carbonate dynamics. Furthermore, many of the impacted harvestable marine species reside below the mixed layer depth while most of the observing system data to date are from the surface waters due to limited availability of sensors suitable for deep-water deployment. The observing design is working increasingly toward collecting biological data from the field to determine if impacts predicted based on laboratory experiments are occurring in the natural environment. This includes the use of standardized CCA accretion plates in the field to determine if CCA rate changes identified in experiments are occurring in coral reefs. Almost half of the assets currently listed on the GOA-ON portal are measuring at least one biological variable (chlorophyll, cyanobacteria/bacteria, zooplankton, and/or phytoplankton). New monitoring indices such as pteropod shell condition are also being explored using repeated ship-surveys along the U.S West Coast. The identification of additional biological variables and integration into the network through cooperation with existing biological observing programs is discussed in the following section. A VISION FOR THE OCEAN ACIDIFICATION OBSERVING NETWORK The observing network should be optimally configured to meet modeling community needs and be fit to purpose. As detailed in the GOA-ON requirements (Newton et al., 2015), the purpose can include detection of OA, whereby assets should be deployed where anticipated time of emergence (ToE) of an OA signal above background natural variability occurs within a few decades in terms of biogeochemical changes, and within perhaps several decades in the case of ecological monitoring (Sutton et al., 2018). This detection requires “climate-quality” data, which involves a more stringent accuracy and precision than may be needed for some applications (Table 1). Models can also assist with determining this metric as long as the primary processes driving the carbonate dynamics are suitably constrained. A well validated or data-assimilated model can be used to extend observations into the past and future. Global-scale models have been used to predict the ToE of an OA signal against the background of other environmental changes (e.g., Gruber, 2011;Carter et al., 2016, 2017;Henson et al., 2017;McKinley et al., 2017). High-resolution coastal models that connect large-scale open-ocean conditions with changes in coastal regions, including coastal upwelling and coral reef systems, are beginning to emerge (e.g., Mongin et al., 2016;Siedlecki et al., 2016;Turi et al., 2016). In locations where the purpose of an OA observing asset is to monitor current conditions, the less stringent “weatherquality” constraints (Table 1) may meet requirements. The observing asset in this case should include a suite of observations that can adequately characterize biogeochemical OA conditions most relevant to applications such as near-real-time support of industry products. Examples include observing systems deployed at shellfish hatcheries at a number of facilities in the U.S. Northwest and Northeast (Barton et al., 2015). This level of data is often available in near-real-time, making it a vital part of forecast evaluation and a key locus of interaction with stakeholders in coastal communities. Additionally, non-sustained deployments should be considered in cases where heuristic algorithm development or mechanistic determinations are the aim. Observing initiatives designated for the purpose of characterizing the primary modes of variability and characterizing it by means of algorithm development and constraint can prove very valuable in scaling direct observations in both time and space. Examples might include flux and rate measurements such as at the benthic interface or investigating mechanisms of predictability to enable Frontiers in Marine Science | www.frontiersin.org 7June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network forecast system development, perhaps by exploring the ways in which large-scale climate variability is communicated to regional waters and watersheds. Observing technologies are becoming more autonomous and highly resolved in time and space, which allows observing networks to become better connected with the coasts and thus communities impacted by the changing ocean. The design and implementation of networks require them to be adaptable, so they are able to continue to evolve with emerging technologies as they become available. Coastal communities will be increasingly affected by changing ocean conditions and forecasts and real-time data access will enable them to develop strategies to respond. The co-location of chemical and biological measurements is needed to assess in situ impacts and helps build the capacity to develop indices, metrics, and risk assessment for coastal ecosystems (Boyd et al., 2015;Bednaršek et al., 2016). The same observing infrastructure should also provide or coordinate with measures of other stressors including temperature change, hypoxia, and pollution that can amplify or attenuate OA responses and influence the physiology, ecology, and the adaptive capacity of marine organisms (Hurd et al., 2018). Next Generation Sensor Technologies to Enhance the Observing System The GOA-ON goal of improving our understanding of global OA conditions will be strongly supported by the development of new sensor technology. Specifically, new technology is needed to quantify (1) the range of natural variability in diverse marine ecosystems (e.g., Figure 6) (Harris et al., 2013); (2) the organismal response to different biogeochemical conditions (Boyd et al., 2015); and (3) long-term trends in biogeochemical parameters. A wide range of in situ measurements are desired but those focused on stressors, i.e., temperature, pCO2, inorganic carbon and pH, oxygen, nutrients, salinity (Breitburg et al., 2015), and biology (biomass, populations) (McQuillan and Robidart, 2017) are high priorities, as discussed in Section “GOA-ON Requirements and Governance.” Accordingly, 10 years ago, OceanObs’09 papers (Borges et al., 2010;Byrne et al., 2010;Feely et al., 2010) called for the development of autonomous sensors and systems to quantify dissolved inorganic carbon (DIC) and total alkalinity (TA). There has been significant progress in this direction with successful in situ deployments of novel DIC and TA instruments (Spaulding et al., 2014;Fassbender et al., 2015; Wang et al., 2015). However, as stated in Byrne et al. (2010), “There are at least two principal impediments to widespread utilization of in situ instrumentation: cost and complexity.” These challenges remain and have limited the widespread use of the new devices. Moreover, even for technologies that have been on the market for several years, data quality varies substantially based on the experience level of the operators (McLaughlin et al., 2017). Continued opportunities for hands-on training, a task that is often initiated by scientists themselves, will be necessary for high-quality data collection and widespread use of new and complex devices. Co-deployment with independent sensors is recommended for new technologies (Bresnahan et al., 2014; McLaughlin et al., 2017), further increasing the cost of obtaining high-quality data. Sensor drift, or loss of accuracy over time, is also a persistent problem. Even when accuracy requirements are relaxed, e.g., for weather quality data in a hatchery, confidence within a defined tolerance must be established. Ideally, sensor data should be validated with independent, in situ samples. Often, conventional methods based on bottle samples collected before and after deployment do not provide sufficient replicates to confidently constrain sensor accuracy. Two highly advanced and widely utilized sensors use innovative strategies to correct for drift. Optode-based O2sensors, a technology that is considered to be mature, have been calibrated by exposing the sensors directly to air (Bittig and Körtzinger, 2015;Bushinsky et al., 2016). ISFETbased pH sensors use deep-water pH values as a pH standard for drift correction (Johnson et al., 2017;Williams et al., 2017). Without these drift corrections for O2and pH, the measurements would not be able to quantify the small seasonal changes in open ocean environments. Simplified technology may be on the horizon. Promising new sensors for pH and pCO2are being developed based on optode time-resolved fluorescence technology similar to O2optodes (Clarke et al., 2015, 2017). Inexpensive, low-power infrared CO2sensors are now being used for oceanographic applications (Bastviken et al., 2015;Hunt et al., 2017). A miniature electrochemical sensor for combined measurements of pH and TA has recently been demonstrated (Briggs et al., 2017). Deployment platforms are more sophisticated and able to accommodate a wider array of sensor technologies (Riser et al., 2018). Profilers include free drifting subsurface floats (Mignot et al., 2018), biogeochemical Argo profilers (Williams et al., 2017, 2018), ice-tethered (wire climbing) profilers (Toole et al., 2011), and moored profilers (e.g., winch operated; Palevsky and Nicholson, 2018). Autonomous underwater gliders and vehicles, self-propelled surface gliders such as Saildrone, and free-floating surface drifters are also becoming more common for oceanographic research in regions not readily accessible by research ships (Lindstrom et al., 2017). Cabled networks with power and high bandwidth data transmission might also become more common in the future. The adaptation of existing sensor technology to more diverse platforms is likely to continue to advance GOA-ON objectives. One additional area that is likely to improve is in our handling of big data sets, both in terms of quality control and the ability to provide real-time diagnostics (Duarte et al., 2018). While it is likely that we will be able to more readily quantify the inorganic carbon system in the coming decade, other important parameters remain out of reach. Dissolved and particulate organic carbon are two critical pieces of the carbon cycle that might be affected by OA (Egea et al., 2018). Optical measurements (fluorescence, absorption) of colored dissolved organic matter are useful proxies (e.g., Jørgensen et al., 2011), but a direct measurement of dissolved organic carbon (DOC) that can be applied to a wide range of marine environments is needed. A major objective of GOA-ON is to quantify relationships between marine organisms and stressors. While most research on biological impacts of ocean change is based on IPCC Frontiers in Marine Science | www.frontiersin.org 8June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network FIGURE 6 | (Top) Distribution of aragonite saturation data (open bars) calculated from in situ pH and pCO2measurements collected over 5 years at the Newport Hydrographic Line mooring (NH-10) off the Oregon coast (United States). The gray and red bars represent estimates from these data using pre-industrial and future CO2levels. (Bottom) The saturation states at the Oregon shelf break at 116 m depth. Adapted from Harris et al. (2013). predictions, new sensor technology reveals existing spatiotemporal complexity of the marine environment that often exceeds the envelope of predicted change (Harris et al., 2013). The variability can influence species responses to baseline changes (Boyd et al., 2016). In addition, and particularly regarding marine benthic organisms, seawater physics and chemistry may significantly vary across small microclimates within habitats. Deployment of arrays of multiple sensors may help characterize these systems (e.g., Leary et al., 2017). Combining sensor data with biology remains an important but very young area of research, and often requires interdisciplinary collaborations or advanced training. New in situ sensor technology might make this more feasible. Future exciting opportunities exist to combine biogeochemical and physical measurements with sophisticated autonomous bio-analytical systems that can characterize and quantify microbial populations (e.g., automated flow cytometry, Hunter-Cevera et al., 2016;in situ genetic analysis, McQuillan and Robidart, 2017). These approaches can potentially overcome the challenge of connecting species biomass or composition with environmental variables by continuously monitoring over a wide range of conditions (Marrec et al., 2018). The discussion above poignantly reveals the challenges we face in developing new biogeochemical and biological sensors. Repeated “technological revolutions” have made us believe that technology will continue to advance indefinitely. Sensor transduction mechanisms, e.g., optical or electrochemical transduction, are mature. Most oceanographic sensors have utilized building blocks from other areas (e.g., fiber optics, integrated circuits) in a combinatorial evolution (Arthur, 2009) to make oceanographic sensors. New building blocks from material science, molecular biology, miniaturization, and fluidics are likely (e.g., Briggs et al., 2017) but will there be new transduction mechanisms that we do not know of today? Filling Gaps in Understanding of Biological Impacts Addressing OA to minimize impacts requires the development of a mechanistic understanding of biological effects. In turn, understanding shifts in ocean biodiversity due to global change requires inclusion of “ocean weather” such as daily and seasonal variability in ocean chemistry, including changes in that variability due to OA (Bates et al., 2018). GOA-ON’s second goal calls for a greater understanding of biological impacts and strong coordination of this research. Reviewing the requirements for biological observations as outlined in Newton et al. (2015), and bridging present and future variability in the carbonate system with ecosystem changes are the objectives of the GOAON biology working group. This group works toward three main tasks: Task 1: Inform the Chemical Monitoring Program About the Biological Needs Marine organisms are often living in highly fluctuating environmental conditions and experience an even wider variability through migrations, changes of environment at different life-history stages or manipulation of their niche. Through local adaptation, species and ecosystems are often able to survive the wide range of variability while stress is induced in conditions deviating from present environmental conditions (Vargas et al., 2017). We need to better capture all the aspects of Frontiers in Marine Science | www.frontiersin.org 9June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network FIGURE 9 | Scheme illustrating the pathways for input to the 2030 Agenda for ocean acidification observations. system, other intergovernmental organizations, international and regional financial institutions, non-governmental organizations and civil society organizations, academic and research institutions, the scientific community, the private sector, philanthropic organizations and other actors—individually or in partnership—that aim to contribute to the implementation of SDG 14. There are currently 247 Voluntary Commitments that address OA, and 61 are of direct relevance to it. The Voluntary Commitments are organized in a Community of Ocean Action. GOA-ON submitted a Voluntary Commitment (#OceanAction16542)21, which includes support for measuring OA, storage, and data visualization by 2020. However, these deliverables will only be accomplished with continuous and increasing financial commitment by countries and organizations to establish and sustain OA observations. The UN Ocean Conference 2020 will be the time to assess achievements from Voluntary Commitments and how to proceed. UN Framework Convention on Climate Change Ocean acidification gained further recognition through its adoption as a Global Climate Indicator in 2018. The Global Climate Indicators are a suite of seven parameters, presented to the UNFCCC, that describe the changing climate in an effort to recognize impacts beyond temperature change. The Indicators include atmospheric composition, energy, ocean, water and the 21https://oceanconference.un.org/commitments/?id=16542 cryosphere. The inclusion of OA in this list shows the importance of guidance to achieve global alignment in observing OA as provided in the SDG target indicator 14.3.1 methodology. CONCLUSION On a global scale, the building blocks of an integrated OA network in the open ocean are well established and quality-control mechanisms are in place (e.g., Climate and Ocean: Variability, Predictability, and Change [CLIVAR]/GOSHIP, OceanSITES, SOCONET, SOOP, SOCAT). However, early consensus of the GOA-ON community is that there is a substantial need for increased observation in many coastal areas, particularly in upwelling regions, regions strongly influenced by freshwater, and coral reef environments (Newton et al., 2015). Components of the open ocean system, including the Southern Hemisphere oceans and the polar seas of the Arctic and Antarctic, are poorly sampled and need enhancement through the application of new technology and optimal use of ships and other observing platforms in the region. For shelf seas and coasts, a global network for assessment of OA is under construction as a high priority for GOA-ON. At the regional level, there are some systems in place with ability to leverage OA observations on existing infrastructure (e.g., World Association of Marine Stations, International Long-Term Ecological Research Network), although many gaps remain. These elements need a globally consistent design, Frontiers in Marine Science | www.frontiersin.org 16 June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network which must also be coordinated and implemented on a regional scale. The Regional Hubs of GOA-ON provide the people-to-people foundation for enhancement of these coastal observations, ensuring that data collected can answer regionally relevant questions. In the coming decade, the GOA-ON will be a critical resource for meeting the SDG 14.3 target, to “minimize and address the impacts of OA, including through enhanced scientific cooperation at all levels” through expert advice and by facilitating the provision of data to support the associated indicator. Building the capacity of countries to submit data to this indicator will be a guiding priority for the GOA-ON Executive Council in the coming years. By facilitating the collection of data in support of SDG 14.3, GOA-ON contributes to the sustainable use of the ocean envisioned by the 2030 Agenda. In addition, a focus on developing better, more reliable, easy to use, and hopefully lowercost technologies for data collection of existing and newly vetted parameters, both autonomously and handheld, will support these SDG efforts. The UN has proclaimed a Decade of Ocean Science for Sustainable Development (2021–2030) to support efforts to reverse the cycle of decline in ocean health and gather ocean stakeholders worldwide behind a common framework, which will ensure ocean science can fully support countries in creating improved conditions for sustainable development of the Ocean. Ocean Science—research and observation—focusing on the impact of multiple stressors on the marine ecosystems, including OA, will be at the heart of the Decade. GOA-ON’s activities will be important stepping stones to develop the mitigation and adaptation strategies for sustainable management of ocean resources. Improving the current knowledge on how OA affects ocean economy is essential to predict the consequences of change, design mitigation, and guide adaptation. Significant progress has been made in the past decade to foster an integrated, leveraged approach to tracking and understanding OA through direct observation. The GOA-ON, a cornerstone of this broader effort, will work to move the community forward to realize this collective vision. Recommendations •Coordination among scientists from a range of disciplines (from chemistry to biology to technology development) and from across the globe including developing regions, particularly by: ◦co-locating chemical and biological measurements to build capacity to develop indices, metrics, and risk assessments; ◦articulating needed biological metrics to chemical monitoring programs; ◦collaboratively evaluating the needs and requirements of a global biological monitoring program; and ◦developing a theoretical framework linking chemical changes to biological responses. •Government, private, and United Nations support for OA observing efforts; •Develop and enhance regional cohorts working together on regionally specific OA issues; •Make observational data from the open ocean to coastal to estuarine systems publicly accessible as much as possible; •Develop capacity so that countries have expertise and guidance needed to report OA data as part of the Sustainable Development Goal 14.3.1 process; •Promote even closer integration between the Global OA Observing Network and other ocean observing networks focusing on related measurements or issues toward this shared vision; •Produce observation-based informational products useful for decision making, such as developing tools and mechanisms to visualize the impacts of OA on marine life; •Optimize the observing system to better support modeling community needs, especially for coastal systems; •New networks should consider prioritizing the following when considering the future of their OA observing networks: ◦to support monitoring that can contribute to Time of Emergence calculations, some data sets acquired should be from the same location, similar time window, and of “climate quality”; ◦to support forecasting and model development, some observations should be prioritized to be real-time or near-real-time; ◦targeted observing initiatives designated for the purpose of characterizing the primary modes of variability that include subsurface observations; ◦co-located physical, chemical, and biological observations to assist in co-stressor and attribution research. •Encourage research to fill gaps in understanding of the biological, ecological, and socioeconomic impacts of OA, particularly by enhanced research on the impacts and interactions of multiple stressors on marine ecosystems; •Promote the development of next generation sensor technology, particularly new technology that enhances ability to quantify: ◦the range of natural variability in diverse marine ecosystems; and ◦the organismal response to different biogeochemical conditions; ◦long-term trends in biogeochemical parameters. •Expand and enhance capacity building efforts to enable broader participation in OA observing and research through: ◦continued growth and support of scientific mentorship activities; ◦further development of regional centers of excellence which can host ongoing trainings and analyze water samples; Frontiers in Marine Science | www.frontiersin.org 17 June 2019 | Volume 6 | Article 337 Tilbrook et al. Global Ocean Acidification Observing Network ◦provision of advanced trainings that include lessons on data quality control and quality assurance; ◦identification and development of accessible, sustainable data hosting platforms; and ◦periodic assessment of global, regional, and local capacity to conduct OA research. AUTHOR CONTRIBUTIONS BT, EJ, MD, JH-A, RF, DKG, LH, KI, MK, JN, SS, and FC contributed to the conception and design of the manuscript and provided text that served as the foundation for the manuscript development. BT, EJ, RF, and JN led the review, the design, and the development of the manuscript, with much assistance from ML, SD, DG, ML, MD, EC, and LK. CP, MG, KS, and MT gathered and incorporated larger community input for the manuscript. All authors contributed to the manuscript revision and have read and approved the submitted version. FUNDING The secretariat support provided by the IOC-UNESCO, the International Atomic Energy Agency, and the NOAA Ocean Acidification Program (OAP) is central to the GOAON effort. GOA-ON also acknowledges NOAA OAP, the University of Washington, U.S. IOOS, and NANOOS for support of the GOA-ON data portal and website, and The Ocean Foundation and government agencies for capacity building and training support. The Climate Science Centre of CSIRO Oceans and Atmosphere and the Integrated Marine Observing System funded the contribution of BT. EJ, RF, DKG, MK, and DG were funded by the NOAA Ocean Acidification Program. MD participation was funded by the U.S. National Science Foundation. JN thanks the University of Washington’s Applied Physics Laboratory and College of the Environment, NOAA OAP, U.S. IOOS, and NANOOS, and the Washington Ocean Acidifdication Center for support for her role in this contribution. MT acknowledges support from the U.S. National Science Foundation grant OCE-1840868 to the Scientific Committee on Oceanic Research (SCOR, U.S.). KI and KS thank the Government of Germany for its financial support to the ocean acidification activities at the Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO). LH contributions were funded by the International Atomic Energy Agency Ocean Acidification International Coordination Centre (OA-ICC), supported by several Member States via the IAEA Peaceful Uses Initiative. MK contributions were funded by the United States Department of State through an IAEA Junior Professional Officer position. The IAEA is grateful for the support provided to its Environment Laboratories by the Government of the Principality of Monaco. ACKNOWLEDGMENTS This community white paper was the collective work of many researchers. 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