Is the fresh water pouring from rapidly melting glaciers changing the seawater in Glacier Bay? If so, what will that mean for marine life…and those who depend on it?
Phase I: 2011 to 2014
Phase II: 2015 to 2018
Melting into Glacier Bay
“Glacier Bay waters may be experiencing ocean acidification on steroids.” – Lewis Sharman, Ecologist, Glacier Bay National Park and Preserve
University of AK Fairbanks biological oceanography professor Russ Hopcroft looks down at the cupful of soupy water in his hand with something very near affection. An expert in zooplankton ecology, Russ is part of a research team on board the vessel Fog Lark. The team is studying ocean acidification in the bay’s waters, in partnership with Glacier Bay National Park and Preserve. In his hand is a concentrated sample of filtered bay seawater. The object of his affection – the thick mass of zooplankton casting about in this water. This is the elixir of life in Glacier Bay.
Russ is one of several researchers analyzing the conditions for life in the seawater lapping at the steep fjord walls of Glacier Bay. Oceans the world over are becoming more acidic as they absorb increasing amounts of anthropogenic CO2 from the earth’s atmosphere. While levels vary from place to place, since the Industrial Revolution, average pH levels in ocean surface waters have decreased by 0.11. Because pH is measured on a logarithmic scale, this means the ocean’s acidity has increased by 30%. Despite this, at a pH of 8.1 seawater is still alkaline, or basic, and thus retains somewhat of a buffer against acidification. (Solutions with pH levels less than 7 are considered acidic). According to Park Ecologist Lewis Sharman, however, Glacier Bay waters may be experiencing ocean acidification on steroids.
Glacier Bay is in the midst of a period of rapid deglaciation. As the glaciers melt, most of this newly liberated glacial water is dumped directly into the bay. Fresh water is typically neutral or even slightly acidic. The greater the volume of fresh water that enters the bay, the more diluted the bay water becomes, and the lower its natural buffering capacity. This process can drive the pH lower.
What are the Impacts?
Living organisms are extremely sensitive to changes in pH levels. Even slight fluctuations can have serious consequences for marine life. A decrease in pH makes it harder to extract dissolved calcium carbonate from the water. Calcium carbonate is used by hundreds of thousands of marine animals, including crabs, shrimp, oysters, and most forms of zooplankton, for shell creation. Without it, this critical task becomes difficult or even impossible. Already the shells of some zooplankton are beginning to dissolve in the more acidic seawater off the coasts of California, Oregon and Washington. The more energy such organisms must expend on shell building, the less they have for other important functions, like growth and reproduction. A compromised shell also leaves individuals more vulnerable to predation. Declines in any dominant species near the base of the marine food web ripple throughout the ecosystem – and beyond. In addition to providing an abundant food source for marine predators, shell-building animals are important components in fish nurseries and serve as natural defenses against storms and erosion (think coral reefs). A diminished shellfish industry could also mean the loss of hundreds of thousands of jobs and an important source of protein for millions of people.
How is the Park Studying the Issue?
In order to determine if this influx of fresh water is affecting pH levels in the bay, the park has embarked on a two-part ocean acidification research project. The first phase took place from 2011 to 2014 and focused on chemical components of the water. The second, which began in 2015 and concludes in 2018, is assessing the direct effects of ocean acidification on the base of the food chain. In particular, they hope to determine if the shells of pteropods, a prevalent zooplankton species that is highly vulnerable to changes in acidity, are corroding and if so, to what degree. They will also be looking to see how zooplankton communities respond to seasonal changes in ocean acidification.
To conduct the study, researchers head out into the bay four to six times a year to collect seawater and plankton samples from 22 permanent stations. Most stations are located along the east and west arms of the bay, with a heavier concentration near the glaciers, where meltwater levels are highest. Two sites are located at the mouth of the bay to measure conditions of the water entering from the open sea.
In both phases of the study, a Conductivity-Temperature-Depth (CTD) probe is lowered into the ocean to measure water temperature, salinity, depth, surface light penetration, dissolved oxygen concentration, and chlorophyll, an indicator of phytoplankton abundance. The probe also collects water samples at pre-determined depths from each station which are later analyzed for levels of dissolved inorganic carbon, alkalinity and nutrient concentration. The results are used to calculate the availability of calcium carbonate minerals to shell-building animals.
In addition to obtaining water samples, plankton nets collect zooplankton from various depths of the bay. Later, Russ and his team will examine these samples under a scanning electron microscope to determine the variety of species present, look for seasonal changes in zooplankton communities and to assess deterioration in the shells of pteropods.
While the study has not yet concluded, preliminary findings indicate that, indeed, Glacier Bay waters are becoming more acidic. It is also apparent that this change is more pronounced in summer and fall, when glaciers are melting fastest, and larger quantities of fresh water are entering the bay.
What this means for Russ’s prized zooplankton and the rest of Glacier Bay’s living organisms should become much clearer in the coming months.
Results from Phase I of the study are available at https://www.nps.gov/articles/oceanacidificationinglacierbay.htm or at https://www.nps.gov/articles/aps-15-1-9.htm.
Deanna Ochs, National Park Service, 2017. Press release.