The Ocean Weather Stations (OWS), established shortly after WWII, were the first sustained network of open-ocean time series sites. These sites, occupied by ships, were meant to support early aircraft routes across the North Atlantic and North Pacific, but they became a valuable source of observations of oceanic and atmospheric parameters at 13 sites in the North Atlantic and North Pacific Oceans. However, the cost of maintaining ships on station was significant; and improvements to weather forecasting and aviation saw the OWS network phased out. The oceanographic community has worked since then to develop moorings to collect time series at fixed sites. Since the 1960s, subsurface moorings have been used to observe ocean currents and water properties. In the 1970s, the first moorings with surface sensor packages came into operation. The first sediment trap was installed on deep-sea moorings in 1978. By the end of the 1980s, regular ship survey based open ocean time series sites were established, e.g., HOTS and BATS.
As the planning for the Global Ocean Observing System (GOOS) went forward, a number of the observing systems organized themselves to coordinate efforts across nations. In conjunction with the 1999 Ocean Obs meeting, advocates of sustained time series sites came together under as the OceanSITES group. The mission of OceanSITES is to collect, deliver and promote the use of high-quality data from long-term, high-frequency observations at fixed locations in the open ocean. OceanSITES typically aims to collect physical, biogeochemical, and biology/ecosystem data worldwide, covering the full-depth water column, the sea floor, as well as the overlying atmosphere. The objective of the OceanSITES observatory network is to ensure the optimal application of the time series technology for a broad a user-base in alignment with GOOS and GCOS principles and policies. Coordination includes documenting the global extent and configuration of the network, and oversight of the scientific and operational communalities across the sites. The standardization of deployment techniques, sensor, and quality control procedures are coordinated through the exchange of knowledge and the documentation of best practices.
One of the main drivers for sustained long-term time series is to provide both monitoring and process observations with a temporal resolution from minutes to decades that will detect, understand, and predict global physical, biogeochemical and ecosystem state and changes, including ocean warming, ocean carbon uptake/storage and acidification, considering also the role of- and impact on, ecosystems. Additional applications of OceanSITES data are, heat storage changes,decadal predictability
changes in ocean carbon (inorganic and organic),
animal tracking, deep ocean observing,
NWP cal/val (boundary layer physics),
particle fluxes (carbon sequestration),
overturning volume and properties transport variability, satellite cal/val,
oxygen inventory changes, sea level changes, deep sea warming.
OceanSITES now reports to JCOMM-OPS as do other elements of GOOS, including the ARGO float program, the GO-SHIP repeat hydrography program, and others. OceanSITES has an executive committee, a science team, and a data team supported by two Global Data Assembly Centers (GDACS). All OceanSITES member have agreed to use a common data format and supply their data as soon as possible to the GDACS, where they are freely available. OceanSITES keeps records of the time series sites and instrumentation and acts to advocate the inclusion of time series sites in GOOS.
During the past several decades mooring and sensor technologies have improved considerably. Today modern moorings host a suite of multidisciplinary sensors that measure key physical, biogeochemical and biological/ecosystems variables. Platform deployments are designed to last several years, hosting surface and subsurface data telemetry systems that may provide data in real-time. One of OceanISTES points for advocacy has been to seek international support for the addition of multidisciplinary instrumentation on existing time series sites; given that these sites already are supported and serviced, this plan would require modest incremental funding.
The OceanSITES network of stations or observatories measures many aspects of the ocean’s surface and water column using, where possible, automated systems with advanced sensors and telecommunications systems, yielding frequent time resolution, often in real-time, while building long records of high-quality data. Locations are optimized to address regional requirements related to sampling ocean phenomena linked among three groups of primary observing objectives:
- The transport-moored arrays (TMA) are optimized for ocean currents and properties observations in sufficient time and space resolution in order to derive volume and property transport estimates. Sampling must be undertaken at a temporal resolution that enables the isolation of drivers of variability, eventually from sub-diurnal to multidecadal. Sites contributing to TMA are, in many cases, arrays of moorings installed in regions where the flow is under topographic control. The major exchange gateways between ocean regions include flows through shallow (e.g. Denmark Strait, Bering Strait) as well as deep straits and channels (e.g. Vema Channel, Gibbs Fracture Zone, Owen Fracture Zone). Another group of TMA sites record western and eastern boundary current flow and properties (e.g. the East Australian Current, California Current) again topography is to be considered in order to ensure a sufficient spatial sampling of the signals.
- The air/sea flux reference sites are located in areas where particular ocean/atmospheric and as such atmospheric boundary layer conditions exists, such as the cold tongue /warm pool regions or the Stratus Deck regions. These sites provide the means to identify errors and biases in gridded surface fields in numerical weather prediction models, remote sensing, and climatologies. Further, these sites provide anchors for the generation of new, improved, hybrid and blended air-sea flux fields. These sites also include observations in areas were air/sea gas exchange processes (e.g. oxygen, pCO2) are in the focus (e.g. deep convection areas).
- The Multidisciplinary Global Ocean Watch sites are located in areas where local ocean Physics, Biogeochemistry and Ecology time series are expected to represent the temporal evolution of a wider area and with consequences that further propagate into the ocean interior. Typically, these sites are in the representative locations of oceanic gyres or biogeographic provinces or where specific forcing is expected, such as deep convection regions.
To facilitate the uptake of OceanSITES data, the program has developed a common data format, OceanSITES netCDF,that is under continuous improvement and expansion by the OceanSITES Data Management Team (DMT) in response to network needs and in dialogue with other global data activities (JCOMM OPA). As technically feasible, some sites transmit data in real-time (via GTS or BUFR format under the auspices of the DBCP). The objective is to produce and share the highest quality long-time series data and distribute it openly and free of charge.
While the plan to broaden the multidisciplinary payload of exisiting OceanSITES moorings has not yet met with support, OceanSITES has been successful with a campaign to add deep T/S sensors to existing sites. This effort has been called the Deep T/S sensor challenge. Deep Ocean observations (below 2000m) have been recognized as an important gap in the global ocean observing system (OceanObs09). At the December 2011 La Jolla OceanSITES meeting, it was decided to make use of the many existing OceanSITES platforms in deep water to make an “instant” contribution towards this need and goal. OceanSITES moorings at over 50 sites already carry deep temperature/salinity (T/S) sensors. After that meeting OceanSITES began to raise funds to purchase a shared pool of deep T/S instruments, with the goal of instrumenting 50 times series sites around the world. OceanSITES was successful in fund raising, drawing mainly upon contributions from lead oceanographic institutions. Together with sensors contributed by the PIs operating the existing sites there is now a global subarray of the OceanSITES sites collecting deep ocean temperature and salinity time series. The group works with the instrument manufacturer to investigate the challenges of making deep T/S time series, to quality control the data, and recalibrate sensors after each deployment. These deep T/S data are submitted to the OceanSITES GDACS.