Long-term Ocean Acidification Moorings

The Need

The ocean absorbs about 25% of the increasing carbon dioxide released into the atmosphere by humans, now roughly 7 million tons of CO₂ every day. As a consequence, seawater is becoming more acidic. Alaska is expected to experience the effects of ocean acidification faster and more seriously than lower latitudes because waters in Alaska are both ‘cold and old’: cooler water temperatures and global circulation patterns mean that Alaska waters naturally hold more CO₂ year round. On top of this high baseline concentration of CO₂, other processes also naturally lower the pH of Alaskan waters on a seasonal scale. Because species can be sensitive to a change in pH, ocean acidification could impact commercial, sport, and subsistence fisheries and wildlife management.

Long time series are important to help us understand interannual variations, including influential factors such as temperature and salinity. By continuing year-round measurements (or during the ice-free season as is the case with M2), we are able to more accurately and precisely study the changes associated with ocean acidification and climate change. Better understanding these processes and documenting the observed changes will help scientists and managers prepare Alaskans for potential impacts to fisheries and livelihoods.

Project Details

AOOS contributes to the maintenance of two long-term moorings located in Resurrection Bay (GAKOA) and in the southern Bering Sea (M2). The buoys have a full package of oceanographic sensors which measure pCO2, pH, salinity, temperature, dissolved oxygen, and florescence.

Using these parameters, the saturation state of aragonite can be determined. Aragonite is a form of calcium carbonate that is critical to shell formation, and the aragonite saturation state provides a unit of measurement for how favorable the water is to shell-building organisms. The buoys record hourly data which is sent in near real-time to scientists at the University of Alaska Fairbanks and NOAA’s Pacific Marine Environmental Lab. Data can also be viewed through the AOOS website.

Project Highlights

Data from moorings quantify the oceans uptake of human released carbon dioxide and the resulting ocean acidification. When paired with models or other ecosystem data it can help identify important natural mechanisms that can exacerbate OA, inform fisheries management, and aid in decision making.

This figure shows the longest, year round record we have in Alaskan waters. Ocean acidification is a long, slow process, taking years of observation to detect a statistically meaningful trend. The GAKOA record is approaching the “time of emergence”, which is how we describe the anthropogenic trend, caused by climate change, that overlays the natural variability in oceanic processes. In coastal environments, with large seasonal variability, detecting the time of emergence generally takes more than a decade of observations (Sutton et al., 2019). Natalie Monacci uses a statistical package (available on GitHub) developed at the NOAA Pacific Marine Environmental Laboratory to determine the GAKOA trend.

Surface mooring observations in Alaska are used in a mapped dataset of ocean acidification indicators for the United States (Sharp et al., 2024). Large marine ecosystems are coastal, hotspots of variability, and influenced by freshwater (which includes glacial melt in Alaska). This effort behind the mapped dataset built an at-a-glance overview of conditions on the National Marine Ecosystem Status website EcoWatch. Here, viewers can choose ocean acidification indicators (carbon dioxide, pH, or saturation state) for a particular large marine ecosystem, as well as compare regions or other indicators and co-stressors such as ocean warming. This tool clearly shows Alaska has some of the most corrosive values (low pH and saturation state) on the indicators, which is why this region is a hotspot for ocean acidification. 

The first model studying ocean acidification in the Gulf of Alaska (Siedlecki et al., 2017) helped build our understanding of how OA works in Alaska. Naturally acidified waters can be brought to the surface, where waters are already affected by anthropogenic impacts. This region also has a unique chemical signature from high freshwater inputs and glacial discharge, which exacerbates OA. This study was fine-tuned and validated with observations from the moorings. Models are an important tool that will help project how OA will impact this region in the future.

Resources

• PMEL’s GAKOA page
• UAF OARC

Principal Investigators