In the kingdom of marine life, the food chain starts with barely visible organisms known as plankton. Small fish devour them, and larger fish feast on small fish. If plankton vanish, all the rest higher up in the pecking order would starve to death.

Some parts of the Arctic now face the danger of losing plankton as sea ice continues to melt, diluting nutrients in the seawater to make it inhospitable for plankton. The ice melt is also accelerating ocean acidification, resulting in a harsher living environment for crustaceans like crabs and shellfishes.

The world’s oceans are a boundless, 3,800-meter-deep expanse with an intricate ecosystem in which its inhabitants and their surrounding environments, from temperature to salinity levels to concentrations and ratios of chemical components, are intertwined with each other. And, in order to understand how these oceans may change due to global warming, we need to first look at the Arctic Ocean as it is one of the areas where most dramatic environmental changes are occurring in the worlds and its conditions have cascading effects on the entire planet.

So, what is really happening inside the Arctic Ocean? And, what will it mean for the world’s oceans that cover 70 percent of the Earth’s surface?

Experts from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) will take you on an Arctic journey for answers.

Heading for the Arctic Aboard Mirai the 8,706-ton Research Vessel

The Mirai, an 8,706-ton research vessel owned by the JAMSTEC, is one of the world’s largest of its kind. It also serves as Dr. Nishino’s research base and home for months on end every year.

The annual voyage that starts and ends in Japan always takes Dr. Nishino and his colleagues through the North Pacific toward the northern Bering Sea first.

“The northern Bering Sea is a treasure trove of marine species, and so we focus on documenting about them as much as possible while moving north,” Dr. Nishino says.

Once through the Bering Strait that separates Alaska and Siberia, the vessel would enter the Chukchi Sea, a biodiversity-rich area in the Arctic Ocean.  The Mirai would then head into the deep Canada Basin.

“This is where some major environmental changes have been happening in recent years,” Dr. Nishino says of the basin. “Sea ice has been melting, and the ocean surface temperatures are rising. We see the seawater becoming more diluted with freshwater, which lowers the nutrient concentration of the water and accelerates the ocean acidification. We gather a wide range of data in this area to keep track of these changes from a macro viewpoint,” says Dr. Nishino, who has also served as the chief scientist for the Arctic research voyage organized as part of the Arctic Challenge for Sustainability (ArCS) in 2016, as well as the previous Arctic cruises in 2013 and 2015.

In addition to oceanographic and atmospheric data, the scientists onboard also collect information related to waves and droplets, greenhouse gas, marine physics, the ocean’s chemical environment, and marine life and benthic organisms ranging from plankton to seabirds.

“Though the Mirai is capable of maneuvering near ice-edge, there are times when sea ice blocks us from what we want to see or measure, or when weather conditions make data-gathering impossible. So, we hold a meeting every day to create a ‘tomorrow menu’ for the next day,” Dr. Nishino says. “Our goal is to use the Mirai to capture the changes occurring in the Arctic Ocean to the best of our ability.”

More freshwater for More Acidic Seawater with Less Nutrients

The Arctic Ocean has two major sources of water: The Pacific Ocean, from which seawater flows in through the Bering Strait, and the Atlantic Ocean. The Pacific water, which is rich in nutrients and plankton, helps enrich the Arctic marine ecosystem.

In recent years, sea ice is melting dramatically in the Arctic Ocean. This means a large amount of freshwater in the Arctic is turning from solid to liquid, diluting the seawater in the surface layer. The nutrient concentration in the surface layer declines (oligotrophication), and the Arctic Ocean’s alkalescent seawater becomes more acidic. These changes all could negatively impact the Arctic marine ecosystem.

But, the domino effect of melting ice doesn’t stop there. Once sea ice is gone, it directly exposes the seawater to the atmosphere. That accelerates the absorption of carbon dioxide in the air into the ocean, which, in turn, exacerbates the acidification of the seawater.

“The Arctic Ocean acidification is advancing at a much faster rate than other oceans are,” Dr. Nishino says.

Changing Oceans as Carbon Dioxide Eater

Oceans absorbs carbon dioxide like a sponge. In fact, one-thirds of anthropogenic carbon dioxide emitted into the atmosphere disappears into the oceans.

When carbon dioxide enters the seawater, phytoplankton that floats near the ocean surface takes in some of them in the process of photosynthesis. Zooplankton eat phytoplankton, which feces and bodies sink to the seafloor to become sediments. This carbon sequestration system known as the “biological pump” effectively removes carbon dioxide from the ocean’s surface and stores it at the bottom.

The problem is, Dr. Nishino says, phytoplankton that plays a crucial role in the biological pump, cannot thrive without nutrients in seawater.

“As the Arctic seawater gets more freshwater mixed in, the nutrients in the surface water become diluted. Plankton populations in the Arctic decline as a result, making it harder for the biological pump to function effectively,” Dr. Nishino says.

Acidification of the seawater might also make the Arctic uninhabitable for organisms that have calcium carbonate shells, including plankton, crabs and shellfishes, as their shells could melt away. In science, calcium carbonate saturation state is expressed with the symbol of Ω. Anything lower than Ω=1 is “undersaturated,” meaning calcium carbonate in shells and bones of living organisms can seep out into the seawater.

“We began to see Ω values for the Arctic surface water dip below 1 in the early 2000s. But, it doesn’t mean shells of plankton, shellfish, crabs and things like that will melt right away. It requires more research to understand how the marine life may adapt to their changing environments,” Dr.Nishino says. (Click here for the JAMSTEC’s press release on the topic.)

Interviewer: Rue Ikeya
Photographs: Yuji Iijima unless noted otherwise
Released on: Aug. 10, 2017 (The Japanese version released on Feb. 10, 2017)