Climate change brews ocean trouble
Scientists tie global warming to increased upwelling of deep ocean water, which can create crippling aquatic dead zones.
from the March 8, 2007 edition
Page 3 of 3
Researchers at Oregon State University have been tracking Oregon's unexpected hypoxic zone since it first appeared in 2002. Last year's event was the worst so far; winds driving the upwelling were twice their usual strength. No one has found a "smoking gun" to connect the hypoxic zone to global warming. But the scientists note that changes in wind patterns driving the plankton blooms that lead to hypoxia are consistent with projected effects of warming. Meanwhile, a team led by John Barth, another Oregon State marine scientist, published a study last month showing that early-season upwelling in 2005 came a month late due to an unusual shift in the jet stream. The delay triggered a serious shortage of nutrients at that led to a dramatic drop in shellfish larvae and juveniles at their usual near-shore "nurseries."
These events show that rising global average temperatures are not the only concern when it comes to global warming's effect on coastal upwelling regions, adds Dr. Barth. "It's also more variance, more variability" in extreme events, he says. If 2005 was extreme in the delayed onset of upwelling, 2006 was extreme in the upwelling's intensity, he says.
But for the University of Miami's Bakun, the poster child for the joint effects overfishing and climate change sits off the Namibian coast. Increased upwelling and overfishing have turned a section of ocean off Luderitz, Namibia, from a habitat once rich in sardines to a malodorous region fit only for jellyfish and other undesirable "weed" species.
Global efforts to move to aquaculture as a path toward sustainable fisheries rely so far on large quantities of fish meal. This comes largely from anchovies off Peru. The region has shown a remarkable ability to reset itself and return to its fecund state as El Niños wax and wane, he observes. But global warming and complex processes unique to marine ecosystems could lead to a tipping point that could turn the region into another Namibia.
"These are complex systems," Bakun says. "And when you change their basic functions, they can run away from you in ways you don't expect."
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