Ocean scientists took their first look Tuesday into the oxygen-starved "dead zone" spreading off the Oregon Coast and were shocked by what they saw: a lifeless wasteland of thousands of dead crabs, starfish and no live fish at all.
"It was a real eye-opener for all of us," said Hal Weeks, a marine ecologist with the Oregon Department of Fish and Wildlife. "I don't think anybody expected this sort of thing."
Dead Dungeness crabs off Cape Perpetua, just south of Yachats, "were like jellybeans in a jar. You just can't count them, there were so many."
Oxygen levels in places along the central Oregon Coast have sunk to the lowest levels ever recorded on the West Coast of the United States, said Francis Chan, a marine ecologist at Oregon State University and the Partnership for Interdisciplinary Studies of Coastal Oceans, an alliance of research institutions.
Scientists suspect swings in the Earth's climate tied to global warming may be shifting wind conditions to bring about such grim results.
Seawater turns deadly for marine life when concentrations of the dissolved oxygen they breathe fall below about 1.4 milliliters per liter. On Monday, Chan measured a concentration of .05, or almost 30 times below the lethal level, about 90 feet below the surface.
It is very close to a complete absence of oxygen, a situation rarely known in the world's oceans, said Jane Lubchenco, a professor of marine biology at Oregon State. New bacteria that take over when oxygen disappears are known to release poisonous hydrogen sulfide gas.
"We never suspected that could happen here," Lubchenco said.
This is the fifth consecutive summer that a layer of low-oxygen water has blanketed the ocean floor along the Oregon Coast, and it has rapidly turned into the most severe episode so far. The layer this year is thicker, lower in oxygen and far larger, covering at least four times more area than in previous years, Lubchenco said...
In the Gulf of Mexico:
Scientific investigations in the Gulf of Mexico have documented a large area of the Louisiana continental shelf with seasonally-depleted oxygen levels (< 2mg/l). Most aquatic species cannot survive at such low oxygen levels. The oxygen depletion, referred to as hypoxia, begins in late spring, reaches a maximum in midsummer, and disappears in the fall. After the Mississippi River flood of 1993, the spatial extent of this zone more than doubled in size, to over 18,000 km2, and has remained about that size each year through midsummer 1997...
Nutrient over-enrichment from anthropogenic sources is one of the major stresses impacting coastal ecosystems. Generally, excess nutrients lead to increased algal production and increased availability of organic carbon within an ecosystem, a process known as eutrophication. There are multiple sources of excessive nutrients in watersheds, both point and non-point, and the transport and delivery of these nutrients is a complex process which is controlled by a range of factors. These include not only the chemistry, but also the ecology, hydrology, and geomorphology of the various portions of a watershed and that of the receiving system. Both the near-coastal hydrodynamics that generate water column stratification and the nutrients that fuel primary productivity contribute to the formation of hypoxic zones. Human activities on land can add excess nutrients to coastal areas or compromise the ability of ecosystems to remove nutrients either from the landscape or from the waterways themselves...
The last time the NOAA was funded to make a throrough update of these man-made oceanic deserts?
November 1, 2000
It seems there have been
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