Nature Climate Change | Climate Feedback

AAAS: Marine mixing, dead zones and climate change

AAAS, Boston –

I went along to the COMPASS ‘marine mixer’ (picture an alcohol-laced gyre awash with journalists and marine science/policy types) last night. In the 7th year now, it has become quite the who’s who of marine science.

At one point, I was chatting to Jane Lubchenco, professor of marine biology at Oregon State University, who is moderating a panel here at AAAS today on the effects of climate change on the ocean.

Lubchenco and colleagues have a brief communication in this week’s scanning video 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…

Olive Heffernan

Comments

  1. Report this comment

    David Smith said:

    Hello. I have a question about wind.

    My understanding is that a warmer US West would lead to stronger winds blowing from west (cool ocean) towards the east (warm land). That, I believe, would decrease upwelling, not increase it.

    Perhaps I am misunderstanding the article.

    Thanks

  2. Report this comment

    jack lang said:

    When I consider how many states affect the Chesapeake, I despair. They blame each other to avoid responsibility. When multiple jurisdictions affect each dead zone, it’s almost impossible to get cooperation.