Alaska’s longest continual ocean acidification mooring just turned ten years old. In lieu of a birthday cake, AOOS partners at the University of Alaska brought the mooring back to shore for its annual maintenance and got it right back out in the water.

Nicknamed “GAKOA” (for Gulf of Alaska Ocean Acidification), the mooring has been a fixture in the waters of Resurrection Bay near Seward since 2013. It has gotten shout outs from tour boat operators and fishing charters, been investigated by sea birds and orcas, and braved high seas and storms. Twice a year, a team from UAF led by Natalie Monacci heads out to care for the mooring.

“GAKOA is a core part of our monitoring in the Gulf of Alaska and we start every new field season at this site,” Monacci said.  “It’s always nice to begin each year with a successful turnaround.”

Throughout this time, GAKOA’s role has been consistent: collect oceanographic data that helps us understand ocean chemistry and change over time. The mooring’s sensors monitor the exchange of carbon dioxide between the atmosphere and seawater, as well as seawater pH, dissolved oxygen, temperature, salinity, and fluorescence.  A nearby oceanographic station known as GAK1 has collected an additional spectrum of data since 1970. These complementary efforts help give researchers insights into ocean physics, biogeochemistry and response to ocean change. 

How is GAKOA’s data useful?

Coastal regions around Alaska are experiencing a rapid onset of ocean acidification compared to other regions, and GAKOA’s record will help communities in Alaska plan for future changes. Ocean acidification is a global phenomenon but manifests differently across regions depending on a mix of local drivers such as water temperature, circulation and salinity. Coastal regions like the mouth of Resurrection Bay experience more variability than the open ocean, with large seasonal and interannual changes. This means a longer dataset is needed to determine trends and drivers of changes in ocean chemistry, attributed to both human-caused and natural processes. Annual data from GAKOA is used in local and international projects, such as ecosystem studies in the Northern Gulf of Alaska and the global carbon budget. Now that GAKOA has a decade-long record, it is approaching the length necessary to assess long-term trends, including anthropogenic (human caused) trends in sea water carbon dioxide, the cause of ocean acidification. Observations at the GAKOA mooring site currently contribute to the United Nations Sustainable Development Goal and the World Meteorological Organization’s climate indicators.   

What have we learned so far? 

• Seasonal change. GAKOA observes a predictable pattern as the seasons change each year.  Surface seawater carbon dioxide is near equilibrium with the atmosphere during the winter months.  In spring and summer, there is a strong drawdown of seawater carbon dioxide during the spring bloom, a time when marine plants are photosynthesizing and using seawater carbon dioxide.    
• Interannual change.  GAKOA observes variability in the timing and intensity of the spring drawdown of seawater carbon dioxide from year to year.  Pairing the CO2 data with the other variables, such as temperature and salinity, is key to linking the site to physical changes in the marine ecosystem.
• Decadal change. GAKOA records the carbon dioxide of both the air and the seawater.  We have observed an increase in the carbon dioxide in the air over our 10+ year record.  The oceans absorb excess carbon dioxide from our atmosphere and we are just beginning to see this anthropogenic trend in seawater carbon dioxide.  We refer to this as the “time of emergence” when human-caused trends emerges from natural variability.       

Partners: University of Alaska Fairbanks, NOAA’s Ocean Acidification Program, Alaska Ocean Observing System, North Pacific Research Board