Ocean pH Dropping 10 Times Faster than Predicted
Marine Food Webs at Greater Risk as Oceans Grow More Acidic
Feb 22, 2009
A study published on November 24, 2008 by the Proceedings of the National Academy of Sciences (PNAS) indicates that the ocean's pH levels fluctuate more widely than expected. However, the study goes on to confirm that, despite these fluctuations, there is still clear evidence that pH levels are dropping in response to increased levels of atmospheric carbon dioxide (CO2).
In fact, the study - "Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset" - reveals that the rate of decline is "substantially faster than predicted by current models and exhibited by the limited data that exist on ocean pH through time."
Increasing Ocean Acidification
The study's authors - J. Timothy Wootton, Catherine A. Pfister, and James D. Forester - examined 24,519 measurements of coastal ocean pH over an eight-year period. The study was conducted as a result of increased concern over ocean acidification, a state in which the ocean's pH drops as a result of absorbing excess CO2 from the atmosphere. The belief by many scientists is that the more CO2 pumped into the air, the more CO2 absorbed into the oceans, and the lower the pH. The study appears to confirm this theory.
Yet the process and degree of acidification is not a simple formula, according to the study's authors. A region's pH can fluctuate 0.24 units in a 24-hour cycle and 1.5 units over the course of a year. And levels can fluctuate from one year to the next. Despite these fluctuations, however, one characteristic is abundantly clear - the pH levels are plummeting - and faster than expected.
Ocean pH levels are affected by many factors, such as the availability of sunlight, the temperature of the water, the amount of phytoplankton, and of course, atmospheric CO2 concentrations. Yet it is the last factor that's causing the greatest concern. Many researchers believe that the ocean pH may drop 0.2 units over the next 100 years, and some believe that the average pH has already fallen 0.1 units over the past century, not surprising given the record amounts of CO2 that has been pumped into the atmosphere.
Threatened Marine Food Webs
But the study does more than confirm what many already accept as fact - that the oceans are becoming more acidic. It also points to the potentially severe impact on ocean food webs.
When pH levels drop, numerous marine species feel the effects, particularly calcifying organisms - such as coral, oyster, and mussel - whose shells dissolve in acidic water. At the same time, other species, like the acorn barnacle or fleshy algae, thrive in these waters, disrupting the natural ecosystem even further.
The study's authors point to the mussel communities that dominate the coasts along the northeastern Pacific Ocean, where mussel beds provide an important habitat on most temperate rocky shores. "These habitats provide food and structure for a diverse array of species in an otherwise physically stressful environment, and the dominant calcareous provide food resources for humans." In addition, mussels affect coastal waters through their filtering activities and play an import role in nutrient recycling.
The mussel has traditionally been seen as being able to tolerate fluctuating environmental conditions. But with the oceans becoming increasingly acidic, the mussel might have met its match. And if such a hearty organism is being threatened by the dropping pH, what does that mean for such habitats as coral reefs and sea grass beds, propagated by species generally considered less tolerant of fluctuation?
The notion that mussel habitat can be impacted by ocean acidification may "portend much broader scale impacts in other marine habitats," suggesting an urgent need for intensive studies of the falling pH levels of the world's oceans - and action that can help mitigate further destruction.
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