APPENDIX: GLOBAL DEEP-OCEAN NETWORKS AND PROGRAMS

A.    OCEANSITES

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.

B.    ARGO/DEEP ARGO/BGC ARGO

The Argo program was first proposed at OceanObs ’99, a decadal conference organized by international agencies with the aim of creating a coordinated approach to ocean observations. Argo was created by a small group of scientists who envisioned a program that would consist of a global array reaching a target of 3,000 active floats within a decade of initiation. Having achieved this goal, Argo is now a major component of the GOOS and exemplifies international collaboration with 31 nations contributing approximately 800 new or replacement floats per year to the effort.

Today, the International Argo Steering Team oversees an array of nearly 4,000 floats and a data management system that delivers consistent quality-controlled data across global data centers. The array delivers 140,000 Temperature/Salinity (T/S) profiles and velocity measurements each year from a series of floats distributed over the global oceans at an average three-degree spacing. Argo floats cycle to 2,000m depth every 10 days, with a typical lifespan of individual instruments of 4-5 years.

All data collected by Argo floats are publicly available in near real-time via the Global Data Assembly Centers (GDACs) located in Brest, France and Monterey, California after an automated quality control (QC). Data are also available in delayed mode within one year after collection after a scientifically vetted quality controlled process[1] (Johnson and Claustre 2016).

During the OceanObs ’09 Conference, the Argo Steering Team released a 10-year report and received input on how the array might be improved. Suggestions included the enhancement of the array to sample the deep-sea and the seasonally ice-covered open ocean.

At the time of the program’s inception, both Argo profiling floats and the accuracy of their temperature and salinity sensors were limited to upper ocean levels (0-2,000 m). However, the scientific community has agreed that a systematic sampling of full ocean depth is necessary to close the global heat and freshwater budgets, constrain drivers of global sea level change, and fully describe the strength and variability of large-scale ocean circulation from the sea surface to the ocean bottom.

A new generation of autonomous floats, referred to as Deep Argo, has been designed to sample the full ocean volume. Models of Deep Argo floats include the Deep SOLO and Deep APEX capable of reaching 6,000 m and the Deep ARVOR and Deep NINJA designed to sample to 4,000 m. Similarly, a new CTD sensor is needed for these Deep Argo floats to go below 2,000 m depth. SeaBird Scientific, is in the process of developing a new CTD sensor that will remain accurate to 6,000 m. This new CTD, the SBE-61, has not yet achieved its ambitious aspirational goals of ± .001 °C, ±.002 pss-78, and ± 3 dbar, but it is progressing rapidly toward them.

Deep Argo is now in a regional pilot, or demonstration, phase with initial arrays deployed in the Southwest Pacific Basin, South Australian Basin, Australian Antarctic Basin, and North Atlantic Ocean. These are all areas with previously observed deep ocean variability. The successful collection of data from these arrays has already provided new insights into deep ocean circulation as well as deep ocean heat storage, freshwater storage, and their sea level contributions. These arrays are the vanguards for implementation of a global sustained Deep Argo array of 1,230 floats with a design target of an active Deep Argo float every 5×5 degrees in waters deeper than 2,000m. The implementation of this array is still several years away in terms of funding and capacity, but the technical readiness level is already high.

[1] www.argo_ucsd.edu/About_Argo

C.    GO-SHIP

GO-SHIP is an international program comprised of a globally coordinated network of sustained hydrographic sections as part of GOOS. It conducts measurements related to physical oceanography, the carbon cycle, marine biogeochemistry and ecosystems. The approximately 62 hydrographic reference sections cover all major ocean basins, from coast to coast, at full depth, with water column and surface water measurements at accuracies required to detect targeted changes.

Historically global hydrographic surveys have been carried out approximately every decade since the 1960s through research programs such as IIOE, GEOSECS, WOCE / JGOFS, and CLIVAR. However, these were one-off surveys with no planned continuity designed to systematically observe changes occurring in the global ocean. In 2009 the Global Ocean Ship-Based Hydrographic Program (GO-SHIP) was established to provide international coordination and scientific oversight of decadal global ocean surveys on a continued basis. In 2015 GO-SHIP added two new classes of hydrographic section to the program – GO-SHIP Associated Sections and GO-SHIP Frequently repeated sections.

The main drivers for these decadal time series are to provide both monitoring and process observations to detect, understand, and predict global physical, biogeochemical and ecosystem state and changes, including ocean warming, ventilation, ocean carbon uptake/storage and acidification. A future goal is to consider the impact of these changes on ecosystems. The specific objectives are:

  • Understanding and documenting the large-scale ocean water property distributions, their changes, and drivers of those changes,
  • Addressing questions of how a future ocean that will increase in dissolved inorganic carbon, become more acidic and more stratified, and experience changes in circulation and ventilation processes due to global warming, altered water cycle and sea-ice will interact with natural ocean variability, and an evolving objective of determining ecological changes.
  • Systematically studying large-scale biogeochemical and ecological decadal changes in the ocean.

Targeted phenomenon to be understood include mixed layer, water mass, heat storage, freshwater cycle, circulation, ventilation, anthropogenic carbon sequestration, storage
ocean acidification.

The GO-SHIP Committee groups GO-SHIP cruises in three different categories and measurements into three priority levels:

  • Level 1 measurements are essential to meet the first two objectives above
  • Level 2 measurements are highly desirable as augmentation and addition for the science objectives executed on GO- SHIP cruises. GO-SHIP recommends that Level 2 measurements should be made when possible
  • Level 3 are ancillary measurements that often benefit from being taken in conjunction with the core measurements and/or address a scientific question unique to the region of investigation. This includes testing of new instruments and approaches. They are collected according to opportunity and space available. They should not significantly interfere with sampling of Level 1 or 2 parameters, and may be regional or specific to an individual cruise.

Cruise categories include:

  • Decadal reference GO-SHIP sections: These are the primary reference lines that meet all sampling requirements including full Level 1 data and comply with the data policy
  • High Frequency GO-SHIP: GO-SHIP lines occupied at higher frequencies (yearly, biennial) with limited parameters, but with at least one decadal reference GO-SHIP occupation (see 1). High frequency cruises must i) occupy the regular line end-to-end, ii) be full depth, and iii) comply with the data policy.
  • Associated GO-SHIP: Repeat hydrographic sections are not necessarily coast-to-coast or coast-to-ice, but meet the following requirements i) deliver high quality data, ii) establish full depth stations below 2000m at least every 240 nm, iii) are repeated on decadal frequency or more, at least once per decade with sufficient level 1 parameters to quantify decadal change in inorganic carbon and heat inventories, iv) at a minimum resolution of 60nm, and v) comply with the data policy.

GO-SHIP is currently the only program that makes systematic and accurate measurements of physical, chemical and biogeochemical Essential Ocean Variables (EOVs) in the deep ocean. The observations from GO-SHIP have yielded the first evidence of temperature and freshwater changes in the deep ocean; they

These measurements form the backbone of observations in the deep ocean. With the advent of new observing technology including platforms such as profiling floats and autonomous sensors our capacities to observe the deep are greatly increasing. The new sensors generally cannot be calibrated in situ, and cannot measure all parameters desirable in DOOS. GO-SHIP provides a means to calibrate the autonomous sensors and to obtain water samples that can be measured for parameters of interest, such as eDNA, and organics, including micro plastics.