Environmental Engineering Reference
In-Depth Information
lower than the pH has been in 20 million years. The extent to
which human activities have raised ocean acidity has been
difficult to calculate because it varies naturally between
seasons, from one year to the next, and among regions and
specific locations. In addition, direct observations go back
only 30 years. If CO
2
emissions continue at the present rate,
often called the business-as-usual scenario, models project
an average worldwide decrease of 0.2-0.3 units by 2100 on
top of what has already happened, doubling the current acid-
ity. The Southern Ocean is an important carbon sink—about
40% of the CO
2
absorbed by the oceans enters there. Rather
than being absorbed uniformly into the deep ocean in vast
areas, CO
2
is drawn down by currents. Winds, currents,
and massive whirlpools (eddies) that carry warm and cold
water around the ocean create localized pathways and acidic
patches.
Reduced pH or ocean acidification (OA) threatens not only
the ecological health of the oceans, but also the economic
well-being of the people and industries that depend on a
healthy productive marine environment. Eutrophication—
algal blooms resulting from increased nutrients (see
Chapter 2)—is another source of CO
2
in coastal waters. When
combined with CO
2
from the atmosphere, the release of
CO
2
from decaying organic matter is speeding up the acidi-
fication of coastal seawater. The pH in the lower part of the
Chesapeake Bay is declining at a rate three times faster than
the open ocean, partly because of nutrients from farming and
other activities. These combined effects make the job of mini-
mizing harmful impacts of OA that much more difficult.
What effects are produced by ocean acidification?
The increased acidity of the oceans is expected to harm a wide
range of ocean life—particularly those with calcium-containing
shells (Figure 9.2). Many organisms use calcium and carbonate
ions from seawater to produce calcium carbonate for shells.
Search WWH ::
Custom Search