Plummeting phytoplankton
Historically, marine phytoplankton has soaked up around 45 billion tonnes of CO2 a year - helping to keep atmospheric CO2 in check. But recently, phytoplankton populations have been in decline. It's yet another reason why levels of CO2 - a greenhouse gas partly responsible for climate change - are on the up.
Scientists at NASA estimate that in the last 25 years global phytoplankton numbers have dropped by at least 6%. The reason? Dust clouds have become less frequent and it's these clouds that carry essential plant nutrients - especially iron - out to sea.
'Wherever you see blue, blue ocean you are essentially looking at a marine desert where no phytoplankton is growing. These dead-zone areas are increasing all the time,' says Russ.
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