Glacier Bay’s Meltwater and Ocean Acidification: What a Park Study Found So Far

Meltwater gushes from beneath Lamplugh Glacier in Glacier Bay National Park and Preserve (NPS).

Glacier Bay is in a period of rapid deglaciation, and most of the fresh water the melting glaciers release goes straight into the bay. Is that water changing the seawater, and if so, what does it mean for marine life and the people who depend on it? Park researchers set out to find out. Park ecologist Lewis Sharman says Glacier Bay waters may be experiencing ocean acidification “on steroids.”

Why meltwater could matter

Oceans everywhere are becoming more acidic as they absorb more carbon dioxide from human activity. Since the Industrial Revolution, the average pH of ocean surface waters has fallen by 0.11. Because pH is measured on a logarithmic scale, the article says, that means the ocean's acidity has increased by 30%. At a pH of 8.1 seawater is still alkaline, or basic, so it keeps somewhat of a buffer against acidification. Solutions with a pH below 7 are acidic.

Fresh water is typically neutral or even slightly acidic. The more of it enters the bay, the more diluted the bay water becomes and the lower its natural buffering capacity, and that can drive the pH lower.

What is at stake

Living organisms are extremely sensitive to changes in pH. A lower pH makes it harder to extract dissolved calcium carbonate from the water, and animals including crabs, shrimp, oysters and most forms of zooplankton use it to build shells. The shells of some zooplankton are already beginning to dissolve in the more acidic seawater off the coasts of California, Oregon and Washington. The more energy these animals spend on shells, the less they have for growth and reproduction, and a compromised shell leaves an individual more open to predators.

A decline in a dominant species near the base of the marine food web ripples through the ecosystem. Shell-building animals feed marine predators, are important in fish nurseries and act as natural defenses against storms and erosion, as coral reefs do. The article adds that a diminished shellfish industry could mean the loss of hundreds of thousands of jobs and an important source of protein for millions of people.

A highly magnified shell of a pteropod, a type of zooplankton, dissolved in seawater adjusted to the ocean chemistry projected for the year 2100 (NOAA).

How the park studies it

The park's ocean acidification project has two parts:

Researchers go out into the bay four to six times a year to collect seawater and plankton samples from 22 permanent stations. Most are along the east and west arms of the bay, with more near the glaciers, where meltwater levels are highest. Two sites at the bay's mouth measure the water coming in from the open sea. The team works from the vessel Fog Lark and includes Russ Hopcroft, a University of Alaska Fairbanks professor of biological oceanography who is an expert in zooplankton ecology, working in partnership with the park.

Zooplankton, typically microscopic, are dense enough to be clearly visible in this cupful of concentrated Glacier Bay seawater (NPS/D. Ochs).

Oceanography stations in Glacier Bay. Red circles mark sites visited twice a year to detect year-to-year variations in water conditions; blue stars mark stations visited on every cruise, whose data help show seasonal variations (NPS).

At each station a Conductivity-Temperature-Depth (CTD) probe is lowered through the water to measure temperature, salinity, depth, surface light penetration, dissolved oxygen and chlorophyll, an indicator of how many phytoplankton are present. The probe also collects water at set depths, which is later analyzed for dissolved inorganic carbon, alkalinity and nutrients. The results are used to calculate how much calcium carbonate is available to shell-building animals.

The CTD probe continuously records the characteristics of Glacier Bay water as it is lowered through the water column (NPS/D. Ochs).

Plankton nets lowered into the bay collect zooplankton from various depths. The team will examine the samples under a scanning electron microscope to see which species are present, look for seasonal changes in zooplankton communities and assess damage to pteropod shells.

Vertical plankton nets are lowered into the bay to collect zooplankton (NPS/D. Ochs).

What they found so far

The study had not yet concluded when the article was written, but preliminary findings indicated that Glacier Bay waters are becoming more acidic. The change is more pronounced in summer and fall, when the glaciers melt fastest and larger quantities of fresh water enter the bay. What it means for the zooplankton and the bay's other living organisms, the article said, should become much clearer in the coming months. Results from Phase I are at https://www.nps.gov/articles/oceanacidificationinglacierbay.htm or https://www.nps.gov/articles/aps-15-1-9.htm.

Sources

• National Park Service, Glacier Bay National Park and Preserve, Monitoring a changing bay, by Deanna Ochs; rewritten in hubnx's own words.