High-latitude Seas “Pre-conditioned” for Increased Acidification; Evidence of Surface Acidity Now Stretches from Hawaii to Alaska
| Marilyn Sigman, Alaska SeaGrant/MAP
Tags: Climate Change, Ocean Acidification, Carbon Cycling, Herring, Alaska Marine Ecosystems, Bering Sea, Gulf of Alaska, Arctic Ocean
Jeremy Mathis, University of Alaska Fairbanks School of Fisheries and Ocean Sciences, gave an opening talk in an Ocean Acidification Workshop and a second presentation during the Alaska Marine Science Symposium.
- High latitude seas are an important indicator for ocean acidification as a consequence of climate change. The cold waters of high latitude regions are naturally low in these carbonate ion concentrations due to the increased solubility of CO2 at low temperatures and ocean mixing patterns. Consequently, saturation states of these minerals are typically lower in polar and sub-polar areas than in temperate and tropical regions.
- In the waters around Alaska, the saturation depth is only 100 m. Water over the Alaska Shelf is “pre-conditioned” for undersaturation. The high productivity following the spring bloom results in high organic matter export and remineralization which adds more carbon into the water. Aragonite undersaturation also results from fresh water runoff and sea ice melt because fresh water is low in carbonates. Thus, additions of anthropogenic carbon and its absorption by the oceanare predicted to result in the acidification of surface waters around Alaska when bottom waters upwell onto the Shelf and into the nearshore.
- Recent data have already documented undersaturation at the surface in the Gulf of Alaska along the Seward Line of moorings in September (thought to be a result of upwellings or the relaxation of downwelling onto the Shelf and remineralization in bottom waters), in the Bering Sea during April in areas of Yukon-Kuskokwim outflow onto the inner Shelf, and during summer over the Continental Shelf in the area of high productivity at the Shelf Edge known as the “green belt;” and in the Arctic Ocean.
- Models project that under current rates of CO2 emissions surface waters of the Arctic Ocean and parts of the sub-arctic Pacific will become undersaturated with respect to aragonite by the end of this century, and, in some regions, as early as 2023.
A research team at the NOAA NMFS Auke Bay Lab explored the physiological effects of acidification on marine fishes with an experiment to determine the effects of lowered pH on survival and growth of Pacific herring embryos. Pre-spawning adult herring were exposed to an array of different carbon dioxide dose levels in a flow-through saltwater system, with pH ranging from 7.94 (ambient seawater) to 6.5. Mortality was dose dependent: the first test mortalities ranged from 2% at pH 7.94 (control) to 88% at pH 6.54; second test mortalities ranged from 0.85% (control) to 14% at pH 6.95. The Length of the embryos at hatching in all treatment groups was significantly smaller than in a control group, suggesting a threshold effect beyond which some impairment of growth took place as embryos used energy for physiological adaptation to the conditions instead of for growth. The researchers concluded that reduced pH depressed the growth and metabolism of developing Pacific herring embryos and mortality increased at the lowest pH levels.
- Increased acidification and changes in the saturation state for calcite or aragonite will affect calcification, thus shell formation for many benthic and pelagic organisms. Mussels, pteropods, and foraminiferans require aragonite; pteropods are an important food item for pink salmon.
Link to Symposium Abstracts.
Distributions and Controls on Ocean Acidification in Alaska’s Marginal Seas
Jeremy Troy Mathis, University of Alaska Fairbanks
Effects of reduced pH on embryonic Pacific herring development: implications for ocean acidification impacts on marine fish (Poster)
Fletcher F. Sewall, NOAA-NMFS Auke Bay Laboratories
Ron A. Heintz, NOAA-NMFS Auke Bay Laboratories
Mark G. Carls, NOAA-NMFS Auke Bay Laboratories
Related Story: USF Study Shows First Direct Evidence of Ocean Acidification
Source: The University of South Florida, 1/20/2010
In a related news story, a team of researchers led by Robert Byrnes, a University of South Florida College of Marine Science chemist, published the results of the analysis of Pacific seawater samples collected between Oahu, Hawaii, and Kodiak, Alaska in the . pH readings were compared from 1991 and from 2006. American Geophysical Union’s journal Geophysical Research Letters. Principal investigator Robert Byrne, a USF seawater physical chemistry professor, said the study leaves no doubt that growing CO2 levels in the atmosphere are exerting major impacts on the world’s oceans.
“If this happens in a piece of ocean as big as a whole ocean basin, then this is a global phenomenon,” Byrne said. Adding carbon dioxide to seawater makes it more acidic, and each year the world’s oceans absorb about one-third of the atmospheric CO2 produced by human activities. Using pH-sensitive dyes that turn from purple to yellow in more acidic waters, the scientists were able to track changes produced by 15 years of CO2 uptake near the ocean's surface, Byrne said. In deeper waters, down to about half a mile, both anthropogenic and naturally occurring changes in CO2 and pH were seen. In the very deepest waters, no significant pH changes were seen.
The researchers found that upper-ocean pH had, over the preceding one-and-a-half decades, decreased by approximately 0.026 units, equivalent to an average annual pH change of 0.0017, over a large section of the northeastern Pacific. Similar recent pH trends have been found at isolated time-series stations in the North Atlantic and Pacific Oceans, and corroborating observations have also been reported by scientists who study other CO2-related substances in seawater.
"The pH decrease is direct evidence for ocean acidification of a large portion of the North Pacific Ocean," said Richard Feely, a member of the research team and chief scientist of the cruise and NOAA researcher from the Pacific Marine Environmental Laboratory in Seattle. "These dramatic changes can be attributed, in most part, to anthropogenic CO2 uptake by the ocean over a 15-year period.” (Feely was also a speaker at the AMSS Ocean Acidification Workshop.)
Corresponding models for the oceans indicate that surface water pH would drop approximately 0.4 pH units, and the carbonate ion concentration would decrease almost 50 percent by the end of the century. This surface ocean pH would be lower than it has been for more than 20 million years. Byrne and many other scientists expect that even if substantial reductions are made in the pace at which humans produce carbon dioxide, ocean acidification will continue for hundreds of years to come.
“The bad news is it takes many hundreds of years for self-correcting factors to occur,” he said. “That leaves many centuries of ugly consequences.”
More of the January 20, 2010, news story