Oceanographic monitoring and research has a long history in the Baltic Sea. The earliest sea level observations started from 1770s (Ekman, 2009). After early German and Swedish expeditions in 1871 (“Pommerania” from Kiel) and 1877 (Swedish expedition by G. Ekman and O. Petterson), the Baltic Sea countries Denmark, Finland, Germany, Russia and Sweden signed in 1892 a resolution on international cooperation in Baltic Sea monitoring and in 1898 an agreement on simultaneous investigations on a regular basis at a few selected deep stations in the Baltic Sea. With the start of the International Council of the Exploration of the Sea (ICES) in 1902 a systematic monitoring of the Baltic Sea was established. In the past two decades, community coordination of the Baltic Sea oceanography has been organized mainly in three areas: marine environment monitoring and protection—coordinated by The Baltic Marine Environment Protection Commission (HELCOM) since 1992, operational oceanography—coordinated by the Baltic Sea Operational Oceanographic System (BOOS) since 1998 and oceanography research related to climate variability and Baltic Sea system science—coordinated by the Baltic Earth program (Earth system science for the Baltic Sea region), the successor program of the Baltic Sea Experiment (BALTEX) since 1993. In addition, fishery monitoring and data management has been coordinated by ICES and DG MARE in the Baltic-North Sea and European scale, respectively. Due to their different mandates, HELCOM members are mainly conducting offline, physical-biogeochemical and biological monitoring for environment assessment, protection, and ecosystem-based management (HELCOM, 2013); BOOS members are mainly responsible for online, physical-biogeochemical monitoring for operational oceanographic services, e.g., forecast, nowcast and hindcast (Buch and Dahlin, 2000; Buch et al., 2006); ICES members mainly carry out offline monitoring ranging from hydrographic to biological parameters for fishery management; ICOS (Integrated Carbon Observation System) is a European research infrastructure to quantify and understand the greenhouse gas balance of the European continent and of adjacent regions and is built up as a collaboration of nationally operated measurement stations in 12 European countries. Most of the monitoring activities in the above categories are regular.

BALTEX/Baltic Earth has a much wider focus. BALTEX was founded in 1993 as a network of operational weather services, climate centers, and universities with the aim to exchange both operational and climate data of the atmosphere, ocean, and land surface and to analyze water, energy and matter cycles in the Baltic Sea region (Raschke et al., 2001; Omstedt et al., 2004, 2014; Reckermann et al., 2011). BALTEX/Baltic Earth is a Regional Hydroclimate Project (RHP) within the Global Energy and Water Cycle Exchanges Project (GEWEX) of the World Climate Research Programme (WRCP). Baltic Earth research aims to fill knowledge gaps of the entire regional Earth system (Meier et al., 2014). However, in this review we limit the discussion mainly to the oceanographic component of Baltic Earth following Omstedt et al. (2004, 2014).

Since their establishments, both BALTEX/Baltic Earth and BOOS have reached significant achievements in their own fields. For operational oceanography, advanced monitoring, and forecasting capacities have been developed at local, sub-basin, and sea basin scales. Observations and forecasts are shared in real or near real time. With sustained observing, the ocean state is identified and new phenomena and related knowledge are discovered and transferred to the operational hindcast and forecast modeling platforms for optimizing existing models; by assimilating observations into the operational models, the capacity on reconstructing historical and forecasting future ocean states is improved. The products generated have been used in marine service for blue economy, ocean health, and climate change adaptation and mitigation (She, 2018a). Currently the BOOS monitoring network provides a significant amount of real time observations from e.g., tide gauge stations, FerryBox lines, mooring buoys, fixed stations, Argo profilers and research vessels (She, 2018b; Siiriä et al., 2018). The quality of operational ocean-ice-wave-biogeochemical models has been significantly improved. Based on the models developed, operational forecasting service has been made both in national and regional levels (She and Murawski, 2018; Tuomi et al., 2018). Data assimilation has been developed to ingrate modeling and observations to derive a better initial field for the forecasting models and reanalysis for reconstructing the history of the Baltic Sea (Zhuang et al., 2011; Fu et al., 2012; Axell, 2013; Liu et al., 2017). Major sources for the development of the operational oceanography in the Baltic Sea have been the Member States. In the past decades, programs from European commission, e.g., Operational Oceanography Cluster in the Framework Programs 5 and 6 (Cieślikiewicz et al., 2007), MyOcean (Bahurel et al., 2010) and following Copernicus Marine Environment Monitoring Service (CMEMS) Program have strongly supported the integration of Baltic Sea operational oceanography in advancing the operational service at the sea basin scale.

Baltic Earth is an independent and open research network with the following vision: “Baltic Earth strives to achieve an improved Earth System understanding of the Baltic Sea region as the basis for science-based management in the face of climatic, environmental, and human impact in the region. Baltic Earth brings together a broad international research community around core scientific issues identified as fundamental to informing societal efforts to achieve sustainability in the region. These “Grand Challenges (GC)” are tackled through joint research efforts, workshops, conferences, and capacity building events accompanied by a continuous process of synthesis of the current state of knowledge. Communication with stakeholders and research funders aims to ensure impact and relevance of the research. Baltic Earth targets the atmosphere, land, and marine environment of the Baltic Sea, its drainage basin and nearby areas with relevance for the Baltic Sea region.” (Baltic Earth Science Plan Writing Team, 2017). Following this vision, Baltic Earth fosters interdisciplinary and international collaboration on processes in the atmosphere, on land and in the sea and also in the anthroposphere by organizing conferences, workshops, seminars, dedicated sessions at conferences, etc. Dedicated working groups (WGs) identify at Baltic Earth conferences and by using assessments of existing research new GCs. Currently, the Baltic Earth community has identified six GCs for the Baltic Earth system research: (GC1) salinity dynamics, (GC2) land-sea biogeochemical linkages, (GC3) natural hazards and extreme events, (GC4) sea level dynamics, coastal morphology and erosion, (GC5) regional variability of water and energy exchanges, and (GC6) multi-drivers of regional Earth system changes. For each of the GCs, WGs were installed. In addition, WGs on outreach and communication, education, and regional climate system modeling are active. A new WG on climate and environmental ocean observing systems such as the Boknis Eck Time-Series Station is in the planning.

Another important aspect of Baltic Earth are thematic assessments that provide an overview over knowledge gaps which need to be filled, e.g., by funded projects. Two assessments of climate change of the Baltic Sea region, which are research community efforts such as the regular assessments of the Intergovernmental Panel on Climate Change (IPCC) of past, present and future climate, have been performed, and a third one is on the way (BACC Author Team, 2008; BACC II Author Team, 2015). Further assessments focussed on Baltic Sea models (Eilola et al., 2011; Placke et al., 2018) and ensembles of scenario simulations with coupled physical-biogeochemical models (Meier et al., 2018a, 2019), both in past and future climates (Meier et al., 2012). Recently, a more comprehensive Baltic Sea Model Inter-comparison Project (BMIP) including also process-based assessments has started.

For the closure of knowledge gaps identified by Baltic Earth assessments, several projects funded by national and European Union (EU) programs have been carried out under the umbrella of Baltic Earth. Selected examples are the BONUS projects AMBER, BALTIC-C, ECOSUPPORT, INTEGRAL, BalticAPP, and SHEBA (see http://baltic.earth). Baltic Earth is coordinated by the International Baltic Earth Secretariat at Helmholtz Zentrum Geesthacht, the Baltic Earth Science Steering Group and the Baltic Earth Advisory Board.

However, the BOOS and BALTEX/Baltic Earth communities had few interactions in the past two decades. Now it is time to enhance cooperation and integration between operational oceanography and Earth system science communities. This is in line with the recent trend of development in several international initiatives such as seamless prediction of the Earth system from the World Meteorological Organization (WMO, 2015) where observing and modeling development at the synoptic scale will be integrated with the climate scale. In the Global Ocean Observing System (GOOS), ocean observing has been extended from mainly for operational service to cover also climate change and ocean health. It is expected that GOOS Regional Alliances (GRAs, e.g., EuroGOOS) and Regional Ocean Observing Systems (ROOSs) will follow this vision to further integrate the ocean observing in operational oceanography, climate change and ocean health fields, as indicated by recent development of a sustained European Ocean Observing System (EOOS, http://www.eoos-ocean.eu). For the assessment and services in climate change adaptation and mitigation, long-term change of extreme events are more and more emphasized which needs calibrated high quality models to perform trustworthy simulations of climate projections.

In addition, the European Commission has asked for “responsive research and innovation” in its research policy in the FPs (Rodriguez et al., 2013; von Schomberg, 2013). Integration and interactions between the operational oceanography community and research community will certainly enhance the responsiveness of our research.

The purpose of this paper is to introduce the state-of-the-art of operational oceanography in the Baltic Sea, set up the scene and identify potential areas of collaboration between the operational oceanography community and the Baltic Earth community. The paper is organized as follows: section Operational oceanography in the Baltic Sea reviews the state-of-the-art of operational oceanography in the Baltic Sea, including operational observing and modeling. Section BALTEX/Baltic Earth marine research reviews the state-of-the-art of Baltic Earth system science while section Operational oceanography and Baltic Earth research—interactions identifies potential collaboration areas between the two communities. Section Discussions and recommendations gives recommendations for future BOOS—Baltic Earth cooperation. Acronyms used in this study are explained in Table 1.

In the following, a few selected research highlights from BALTEX/Baltic Earth are presented, documenting the progress in physical oceanography of the Baltic Sea during 2003–2014 (Omstedt et al., 2004, 2014; see also BACC Author Team, 2008; BACC II Author Team, 2015) and after. One of the main motivations for the foundation of BALTEX in the 1990s was the exchange of data between eastern and western Baltic Sea countries. Due to the Iron Curtain after World War II, the exchange of scientific information was limited. Hence, after the rise of the Iron Curtain in the 1990s BALTEX aimed to enhance international collaboration between the Baltic Sea countries and to increase the exchange of especially observational data.

The Baltic operational oceanography community and the BALTEX/Baltic Earth community have co-existed in the past two/three decades. However, only very preliminary interactions have been carried out because differing objectives of both communities hampered an intensive collaboration as outlined below.

Through analysis of the state-of-the-art of operational oceanography and regional Earth system research, it was found that the operational observations, modeling platforms, and products can significantly benefit the Baltic Earth research, e.g., in the areas of the six grand challenges, while the Baltic Earth research can also benefit operational oceanography. Most of the research databases such as the Baltic Environmental Database (BED, http://nest.su.se/bed) at Stockholm University, the Swedish Ocean Archive (SHARK, http://sharkweb.smhi.se) and all other environmental databases operated by the Swedish Meteorological and Hydrological Institute (SMHI) and the German Baltic Sea monitoring data archive (IOWDB, http://iowmeta.io-warnemuende.de and https://odin2.io-warnemuende.de/) operated by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) are already open access. In the future, a common database including both operational and research data may be established. In Europe, EMODnet has integrated marine observations, both online and offline data, in the entire parameter domain ranging from physical, biogeochemical, biological to human activities. In future, it may play a more important and active role for linking research observations and operational oceanography. However, for the research of, for instance, detecting ocean changes high accuracy of measurements is needed which is today not assured by all operational data products. The calibration of measurement devices is time consuming and expensive. Quality control is also the reason why not all research data of IOWDB and other databases can be provided in real or near real time.

Research observations can be an important complementary in emerging observations for developing operational ecology, predicting the fate of visible, and invisible marine plastics in the Baltic Sea, modeling and forecasting sediment transport, underwater noise etc. For these areas, operational observing capacity has not been established yet. They will need to heavily rely on data from research projects.

As mentioned above, reanalysis data sets are useful for climate analysis and for the evaluation of climate models used within Baltic Earth. However, current reanalysis data sets are usually not based on first principles, i.e., the conservation of mass, energy and momentum. Hence, many data assimilation schemes may cause problems, for instance, for budget and flux calculations of nutrients (Liu et al., 2017). This may lead to problems when using reanalysis for trend and long-term variability analyses. Hence, reanalysis products should be improved for the climate research purpose by using more mass and energy conserved assimilation method, e.g., 4D variational assimilation.

Research observing infrastructure should be made more usable for various applications. Examples of observing systems that fulfill such a criterion are the Australian IMOS (Integrated Marine Observing System, Hill et al., 2009) system, the German COSYNA (Coastal Observing System for the Northern and Arctic Seas, Baschek et al., 2017) and the IOW long-term monitoring program outside the German territorial waters. Although funded as a research infrastructure, the programs provide openly accessible observations, which can be used for many other purposes. These systems have been operated for more than 10 years.

The new knowledge made from the Baltic Earth research, both on the processes and model system development, can be transferred to the operational models, which will fill the knowledge and technological gaps in the operational modeling. The two communities should have regular joint meetings to identify topics with common interests and make the technology transfer from regional Earth system research to operational oceanography. For such a working group Baltic Earth would provide an ideal discussion platform. Unfortunately, state-of-the-art climate and operational ocean model versions usually differ although some institutes aim to have only one version for both applications. However, in reality two model versions are still needed because not all processes are well-enough understood such that their parameterizations fulfill the requirements of both applications on short and long time scales. An example is diapycnical mixing. Climate models require that long-term simulations do not artificially drift whereas data assimilation can always compensate shortcomings in operational mode. The development of operational oceanography in the last two decades, by integrating field monitoring, research (knowledge generation), operation and service, has demonstrated successfully the value chain of ocean research. In the Baltic Sea region, the future research is moving to an Earth system scale and be more responsive, the operational and adaptive level of the services for marine, climate, environment, and fishery are evolving. The value chain practiced by the operational oceanography is similar to other areas, e.g., Earth system research and environment protection. Seamless monitoring, modeling, and service provides a unified platform for integrating the research and services.

Next generation operational service system needs capacities on reconstructing, forecasting and projecting the states of marine ecosystems in basin and coastal waters. Significant new knowledge is needed for understanding and forecasting ocean processes such as inter-basin and sub-basin transport, sub-mesoscale eddies, coast-estuary interaction, sediment transport, algae bloom, oxygen depletion, and marine litter transportation. An idea solution is to carry out monitoring-modeling integrated and targeted research programs in the Baltic Sea scale (She et al., 2016). Joint force from BOOS and Baltic Earth community is a great advantage for responsive and collaborative research on the development of seamless service capacities, from synoptic to climate scales, from open sea to local waters, from physical to biological subsystems. During the procedure, scientific issues e.g., Baltic Earth GCs and interactions and coupling between different subsystems, will be addressed. Well-designed research programs should cover not only dedicated field experiment and new knowledge generation but also knowledge transfer into seamless operational model system and product service.

Naturally BOOS and Baltic Earth will consider to engage other important Baltic networks such as HELCOM, ICOS, and ICES in their cooperation as Baltic Earth and BOOS already collaborate with them. Within EN CLIME Baltic Earth and HELCOM are working together to produce a climate fact sheet and HELCOM and ICES representatives are members of the Baltic Earth Advisory Board. In the upcoming EuroSea project, BOOS and HELCOM partners will work together on improving fast delivery of HELCOM data to BOOS and a delivery of a better reanalysis to HELCOM by BOOS to assimilating HELCOM data. HELCOM is also an important stakeholder for both BOOS and Baltic Earth communities. Many projects carried out by BOOS and Baltic Earth partners, such as Baltic Sea Check Point, CLAIM, ECOSUPPORT, address HELCOM goals. HELCOM monitoring is an important source of biogeochemical and biological (lower trophic level) observations for both research and operational services. Carbon observations from ICOS and biological observations collected by ICES are important to BOOS future priority on operational ecology and Baltic Earth System studies.

All authors contributed in writing, with JS as lead author and main author on operational oceanography, HM as main author on Baltic Earth and VH as main author on BAL MFC.