Aquecimento global e mar

O blogue Climate Feedback dá notícia sobre as zonas (biologicamente) mortas nos oceanos (ver terceiro item aqui), na seguinte nota: Marine mixing, dead zones and climate change. Transcrevo abaixo, parte do apontamento (a bold estão indicados os links a que se pode aceder nesse blogue):

Lubchenco and colleagues have a brief communication in this week’s scanning vídeo footage off the seabed off the Washington and
Oregon coast, Lubchenco and her fellow marine ecologists came across a mass of
dead marine organisms. After some investigation, they found this was due to the
expansion of a dead zone both toward the coastline and throughout 80% of the
water column. The region, known as the California Current Large Marine
Ecosystem, is one the world’s four eastern boundary current systems, which are
some of the most productive areas in the ocean and produce 20% of the world’s
fisheries.

The number of such ‘dead zones’ throughout the world’s oceans
has increased dramatically in recent decades. Most, however, such as the
well-known Gulf of Mexico dead zone, are caused by excessive nutrient run-off
from land increasing the nitrogen content of the water, and sucking out the
oxygen. Under normal conditions, the region off the US west coast is
characterised by the upwelling of nutrients from deep waters, driven by strong
winds. Plentiful nutrients provide the nutrition necessary for an algal bloom,
which forms the basis of a rich food web. But too much nutrition…and it all goes
horribly wrong.

Lubchenco and colleagues believe that warming of the land in the western US is
now causing the winds to persist for longer, prolonging the upwelling…and with
it, the algal bloom. Instead of feeding phytoplankton, the bloom becomes coated
in bacteria, decays and ends up on the seafloor, where it release nasty gases
and poisons fish. Lubchenco says she believes that the same patterns could be
occurring in similar systems elsewhere, such as the Benguela current off the
coast of South Africa, where dead zones are also expanding. Yet another
unexpected consequence...