Research by scientists of America's Oregon State University has established that, in various parts of the world, changes are occurring in marine currents rising from oceanic depths.
The currents are responsible for bringing water rich in nutrients closer to the surface, leading to the creation of plankton blooms which support food chains in shallower oceanic waters and on coasts.
Disruption of the currents has, say the researchers, led to 'dead zones' off the coasts of several countries, with catastrophic falls in numbers of marine species and seabirds. Changes in wind patterns which normally blow any plankton shoreward are also thought to have contributed to the problem in coastal areas.
Affected regions listed are seaboards of the western US, Chile, South Africa and Namibia. The problem has developed particularly over the past five years.
For example, say the researchers, in 2005 a delay in oceanic upwellings along the western US caused a collapse in fish populations, such as migrating salmon.
In 2006 the pendulum swung the other way, with upwellings so extreme that super-thick plankton blooms sank back down, stripping the water column of oxygen. Marine creatures suffocated, leaving a dead zone of some 1150 square miles. |
