Melting ice could mess up deep sea chemistry

Melting glaciers might be making ocean water more acidic, an unexpected finding that’s given scientists new cause for concern.

A new study published yesterday in the journal Nature Climate Change suggests surprising ways that climate change is drastically altering the water chemistry in deep seas—a process that may happen faster than researchers anticipated.

The threat of ocean acidification has drawn increasing attention in recent years. The ocean absorbs a substantial amount of the carbon dioxide that humans emit into the atmosphere—and when carbon dioxide goes into the sea, a chemical reaction occurs that causes the water to become more acidic. That’s a big concern for marine biologists, as research suggests that the decreasing pH levels could disrupt the ability of corals, mollusks and other marine organisms to build the hard outer shells they need to survive.

Because humans are still emitting about 40 billion tons of carbon dioxide into the atmosphere each year, ocean absorption of greenhouse gases from the air remains the primary concern about acidification. This process mainly affects the water close to the surface, where the gases are actually being absorbed.

But as the new research points out, dead plants and animals also release carbon dioxide as they drift to the bottom of the sea and decompose. Deep ocean currents can help to move the carbon dioxide throughout the water so it doesn’t sit in one place. But some scientists believe that certain effects of climate change—including the influx of cold, fresh water from melting glaciers, or an increase in the heat absorption as sea ice disappears and exposes the water to the sun—may eventually disrupt these currents or cause them to slow down.

Now, the new study’s authors suggest this process could speed up the acidification of the deep seas. In fact, their new research suggests this process may already be occurring in the Sea of Japan, a 380,000-square-mile body of water between Japan, North and South Korea, and Russia.

Like the open ocean, the Sea of Japan contains special currents that carry water from the surface down to the bottom of the ocean, a kind of mixing process known as “overturning circulation.” (The same process occurs on a much larger scale in the open ocean, where huge currents act as a kind of conveyor belt carrying warm water from the equator to the poles and vice versa.) But over the past decade or so, several studies—among them a study published in October 1999 in Geophysical Research Letters — have already suggested that the overturning circulation in the Sea of Japan may have begun to slow down during the 20th century, perhaps due to the influence of climate change.

In the new paper, the scientists analyzed 50 years of collected data on water chemistry in the Sea of Japan, from 1965 through 2015. They found that the deep waters have, in fact, been growing more acidic—and the acidification rate is 27 percent higher than the rate occurring at the surface, a “truly noteworthy” finding, according to Christopher Sabine of NOAA’s Pacific Marine Environmental Laboratory, who published a comment about the new research in Nature Climate Change yesterday.

The researchers suggest that the Sea of Japan could serve as an analog for the oceans at large, a warning of the kinds of effects that may occur on a larger scale as climate change continues to progress. It’s not a perfect comparison, Sabine cautioned—the Sea of Japan is small, and its circulation processes are much less complex than those in the open sea—but he noted that the work “suggests that a significant anthropogenic effect on deep-ocean acidity could be in store for the future and should be considered as part of the suite of anthropogenic impacts on the ocean.”

If this is the case, the new study may add weight to a growing list of concerns about the effects of ocean acidification on marine ecosystems. In October, a German research consortium known as BIOACID released a report summarizing eight years of research on ocean acidification, concluding that the process has many negative effects on marine organisms, which may not be able to adapt fast enough to survive in the future. The report suggested that the findings constitute a “strong case for limiting climate change.”

And earlier this month, at the U.N. climate conference in Bonn, Germany, members of the International Alliance to Combat Ocean Acidification — which include the states of California, Washington and Oregon; the Canadian province of British Columbia; and nations including Fiji and Sweden—reaffirmed their commitments to developing action plans aimed at limiting acidification.

The absorption of carbon dioxide straight from the atmosphere may rightfully remain the primary threat to the ocean’s pH. But the new study highlights another, less obvious manner in which climate change could threaten ocean chemistry, suggesting that curbing greenhouse gas emissions may actually combat ocean acidification in multiple ways.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.

Chelsea Harvey, Climate Wire, 28 November 2017. Article.

 

 

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Ocean acidification in the IPCC AR5 WG II

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