Posts Tagged Arctic Ocean

Nov 13 2015

NOAA Finds Arctic Ocean, Northern Pacific and Antarctic Waters Acidifying Fastest

— Posted with permission of SEAFOODNEWS.COM. Please do not republish without their permission. —

Copyright © 2015

Seafood News

SEAFOODNEWS.COM [Alaska Dispatch] By Yereth Rosen – November 13, 2015

The Arctic Ocean and the northern Pacific Ocean, along with Antarctic waters, are acidifying faster than the rest of the world’s marine waters, a new National Oceanic and Atmospheric Administration-led study finds.

The study, which analyzed measurements from thousands of monitoring stations across the globe, found these bodies acidified faster as carbon dioxide absorbed from the atmosphere combines with natural sources of carbon swept into them by marine currents and held fast by low temperatures.

Ocean acidification is the chemical transformation seawater undergoes as it absorbs and stores more carbon. The increasingly acidic water more easily dissolves the calcium carbonate from which many marine species make their shells — affecting not only commercially important shellfish, such as oysters and clams, but also smaller creatures, such as tiny pteropods, upon which marine food webs depend. That could upend entire ecosystems, harming other important species, including salmon.

The new study, published online in the journal Global Biogeochemical Cycles, uses data from 11,431 sampling stations to evaluate aragonite saturation levels in oceans worldwide — the degree to which aragonite, a form of calcium carbonate that sea creatures use to build shells, is held in the water.

When water is saturated, it holds the maximum amount of dissolved aragonite. When it is supersaturated, it holds excess suspended aragonite. All the world’s oceans, measured down to a depth of 50 meters, are supersaturated with aragonite, according to measurements from the Global Ocean Data Analysis Project used in the study.

Still, those measurements and other large-scale programs monitoring ocean conditions, show that aragonite saturation levels have slipped globally, a troubling sign, the study’s lead author said.

“A decline in the saturation state of carbonate minerals, especially aragonite, is a good indicator of a rise in ocean acidification,” Li-Qing Jiang, an oceanographer at NOAA’s Cooperative Institute for Climate and Satellites at the University of Maryland, said in a statement issued by the agency.

The study found that at depths shallower than 100 meters, aragonite saturation levels declined by an average rate of 0.4 percent a year from the decade spanning 1989 to 1998 to the decade after then, spanning the years 1998 to 2010.

Low levels of aragonite saturation were pronounced in the North Pacific Ocean at latitudes above 50 degrees north, according to the study. At depths of 200 meters and below, all the sections measured in that part of the Pacific showed undersaturated states for aragonite, the study said. Aragonite undersaturation, a condition normally found in the very deep parts of the world’s oceans, can be a troubling sign when it occurs in shallower waters, scientists say.

The Arctic Ocean also showed lowered aragonite saturation states, though not as low as those at corresponding depths of the North Pacific. Less data was available from the Arctic Ocean, researchers noted.

In contrast, the Atlantic Ocean was found to have aragonite-supersaturated waters down to much deeper levels, thanks to a lower level of lingering carbon from decaying organisms, according to the study.

“The deepest saturation horizon and youngest water are found in the North Atlantic. The shallowest saturation horizon and oldest deep waters are found in the North Pacific. This is because older water has had more time for CO2 accumulation from organic matter remineralization,” the study said.

In the polar regions, even the surface waters — though supersaturated with aragonite — held far less of the mineral than did waters in more temperate latitudes, the study found.

The Arctic, Antarctic and North Pacific are vulnerable to acidification in part because of their cold waters, which hold in carbon dioxide, the study said. Those regions, along with some other marine areas in the world, such as a region off the coast of Africa, are more vulnerable because the pattern of ever-moving ocean currents brings in carbon-dioxide-rich waters from elsewhere in the world and causes that older water to rise up to shallower levels closer to the surface, the study said.

That’s especially the case in the fish-rich North Pacific, site of major Alaska-based commercial seafood catches, which has the distinction of being at the very end of the Global Thermohaline Circulation, the pattern sometimes called the “ocean conveyor belt,” Jiang said in an email.


Jan 27 2015

Atlantic, Pacific Fish Face Mixing as Arctic Warms


The gradual warming of the Arctic Ocean over the next century will weaken a natural barrier that has separated fish from the Atlantic and Pacific Oceans for millions of years, leading to a mixing of species that could make life difficult in fishing communities from Alaska to Norway.

A new study by scientists in Denmark combined current models of climate change, and the biological water temperature and food requirements for 520 fish species native to the two oceans. The report forecast changes in the range of these fish in five-year increments from now until 2100, when the world’s oceans are expected to heat up globally by an average 4 degrees Celsius (7 degrees Fahrenheit).

“There will be an interchange of the fish communities between those two seas,” beginning as soon as 2050, said Mary Wisz, lead author on the report in Nature Climate Change and a senior ecosystem scientist at Aarhaus University in Denmark. “We know from historical examples that this kind of interchange, when biotas have been separated over long evolutionary time scales, can have huge consequences.”

In this warmer future, fishermen based in Kodiak, Alaska, could be pulling up Atlantic cod, a prized species normally caught off New England and Northern Europe. A similar change has already started off the coast of Greenland, where fishermen in the last five years have been catching larger numbers of Atlantic mackerel, which prefers more temperate water.

Wisz and colleagues say that by 2100, up to 41 species could enter the Pacific and 44 species could enter the Atlantic, through Arctic water passages over Canada or Russia. This interchange will have ecological and economic consequences to ecosystems that at present contribute 39 percent to global marine fish landings.

While some fishermen may benefit from the new catches, scientists warn that it’s hard to predict exactly what kind of fish will take over, and which will be driven away by the newcomers. It’s also possible that several kinds of fish could compete for the same food source – smaller fish, marine shrimp or larvae, for example, leading to a big reshuffling of the existing marine food chain.

“Some species when they come together they get along,” said Peter Moller, curator of fishes at the Natural History Museum of Denmark and another author on the new report. “But of course the Atlantic cod has the potential to become extremely numerous and dominating if it has the right conditions. There is speculation if it gets to a new place, it can be a real game-changer.”

Moller said the cod is an especially voracious predator of smaller fish, and could impact commercial landings of Alaska Pollock, for example. Around 3 million tons of Alaska pollock are caught each year in the North Pacific from Alaska to northern Japan. Alaska pollock is the world’s second most important fish species in terms of total catch.

Jason Link, senior scientist for ecosystem management at the National Oceanic and Atmospheric Administration, agreed that the mixing of species will cause changes in the food web in both oceans, but it’s hard to predict exactly how it will shake out.

“Another issue not noted in this paper is what happens in the ecosystem that these fish move out of, do they remain there or do other species replace them from the south?” Link said via e-mail.

Another thorny issue is how to manage fishing boats who will likely be plying the rugged Arctic Ocean once commercial harvests become feasible.

“This work raises important ramifications for fishes in response to changes in sea ice,” Link said.

Wisz and Moller say their next task is to look at realistic scenarios of predators and prey in the new warmer Arctic ecosystem.

Read original post here.

Sep 12 2013

Unprecedented Rate and Scale of Ocean Acidification Found in the Arctic

ST. PETERSBURG, Fla. — Acidification of the Arctic Ocean is occurring faster than projected according to new findings published in the journal PLOS ONE.  The increase in rate is being blamed on rapidly melting sea ice, a process that may have important consequences for health of the Arctic ecosystem.

Ocean acidification is the process by which pH levels of seawater decrease due to greater amounts of carbon dioxide being absorbed by the oceans from the atmosphere.  Currently oceans absorb about one-fourth of the greenhouse gas.  Lower pH levels make water more acidic and lab studies have shown that more acidic water decrease calcification rates in many calcifying organisms, reducing their ability to build shells or skeletons.  These changes, in species ranging from corals to shrimp, have the potential to impact species up and down the food web.

The team of federal and university researchers found that the decline of sea ice in the Arctic summer has important consequences for the surface layer of the Arctic Ocean.  As sea ice cover recedes to record lows, as it did late in the summer of 2012, the seawater beneath is exposed to carbon dioxide, which is the main driver of ocean acidification.

In addition, the freshwater melted from sea ice dilutes the seawater, lowering pH levels and reducing the concentrations of calcium and carbonate, which are the constituents, or building blocks, of the mineral aragonite. Aragonite and other carbonate minerals make up the hard part of many marine micro-organisms’ skeletons and shells. The lowering of calcium and carbonate concentrations may impact the growth of organisms that many species rely on for food.

The new research shows that acidification in surface waters of the Arctic Ocean is rapidly expanding into areas that were previously isolated from contact with the atmosphere due to the former widespread ice cover.

“A remarkable 20 percent of the Canadian Basin has become more corrosive to carbonate minerals in an unprecedented short period of time.  Nowhere on Earth have we documented such large scale, rapid ocean acidification” according to lead researcher and ocean acidification project chief, U.S. Geological Survey oceanographer Lisa Robbins.

Globally, Earth’s ocean surface is becoming acidified due to absorption of man-made carbon dioxide. Ocean acidification models show that with increasing atmospheric carbon dioxide, the Arctic Ocean will have crucially low concentrations of dissolved carbonate minerals, such as aragonite, in the next decade.

Read the full article here.