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Gulf of Alaska Ecosystem Observatory (GEO)


Moored dataloggers in the Gulf of Alaska now collect high-resolution biological, physical, and chemical data year-round. Although co-located and multi-disciplinary time series data are rare for any continental shelf, understanding time-dependent marine processes and ecosystems requires measurements like these.


In the NGA region, over 20 years of ship-based expeditions have tracked environmental changes from season to season. However, few oceanographic observations have been made between October and March off-shore from oceanographic station GAK1.

Additionally, few observations are made at time scales that are important to the plants and animals that live there. For example, we know little about the rapid changes that take place over hours, days, and weeks. And we know little about the transformations that take place as the marine system “resets” itself in winter.

Location of GEO
Map of the Gulf of Alaska showing the location of the Gulf of Alaska Ecosystem Observatory (GEO, red star) relative to the Seward Line (white)
Prepping GEO
Installation of sensors on the surface buoy of GEO3-2019 on the back deck of R/V Sikuliaq [credit: Gwenn Hennon]


To solve the problem of the under-sampled ocean, we have deployed a moored ecosystem observatory – an array of 3 moorings measuring diverse parameters. The collected data probe the inner workings of the marine ecosystem from the perspectives of multiple disciplines, multiple trophic levels, and multiple time scales. We measure:

  • Ocean currents, atmospheric winds, temperature, and salinity, which regulate ocean stratification;
  • Light and nitrate, which fuel phytoplankton growth;
  • Chlorophyll-a fluorescence, optical backscatter, and dissolved oxygen, which provide measures of phytoplankton biomass and respiration;
  • Fluxes of particulate carbon to the seafloor, which supply the benthic community with organic matter;
  • Presence and density of nekton (i.e. fish and mesozooplankton), through the use of acoustic backscatter;
  • pCO2 and pH, which mediate ocean acidification; and
  • Vocal marine mammals, vessel noises, and other underwater sounds by a passive acoustic recorder. Here listen to some recorded killer whales:


With our long-term and high frequency measurements, we can observe changes in the NGA’s fresh water, nutrient, and carbon cycles. Similarly, we can observe the timing and location of zooplankton and fishes. Because these moorings will be out for years, we’ll see how changing wind, waves, and currents affect the regional oceanography.

This mooring has many links to other studies in Alaskan waters. For example, a companion observatory to GEO is the Arctic Chukchi Ecosystem Observatory (CEO) that is deployed in the Chukchi Sea (2014-present). And by linking the moored samples with the NGA LTER ship-based samples, we will achieve a fuller picture of the NGA ecosystem.


Operational support for GEO has been provided by the NSF Northern Gulf of Alaska (NGA) Long-Term Ecological Research (LTER) project. Support for observatory equipment has come from the M.J. Murdock Charitable Trust, the Alaska Ocean Observing System (AOOS), the Exxon Valdez Oil Spill Trustee Council’s (EVOSTC’s) Gulf Watch Alaska (GWA) program, NPRB’s Long-term Monitoring (LTM) program, and the University of Alaska Fairbanks (UAF).


Murdock Trust logo

Access to Real-Time Data

In 2019, three moorings were deployed. Two surface buoys included a sensor package from PacificGyre that transmitted meteorological and oceanographic data in real-time via an Iridium satellite link. These data are available for viewing and downloading in real-time courtesy of the data portal of the Alaska Ocean Observing System.

In subsequent years, the buoys were redeployed. Only GEO3 continued the real-time feed. Here are the links to that real-time data:

GEO data screenshot
Screenshot of real-time data feed from the GEO mooring. [AOOS/Axiom Data Science]