Environment analyst Roger Harrabin said: 'The researchers don't know if the change is due to climate change or to natural variations'.
'But they say it is a tremendous surprise and very worrying because there were grounds for believing that in time the ocean might become 'saturated' with our emissions - unable to soak up any more,' the BBC quoted him as saying.
Of all the CO2 emitted into the atmosphere, only half of it stays there; the rest goes into carbon sinks.
There are two major natural carbon sinks: the oceans and the land 'biosphere'. They are equivalent in size and absorb a quarter of all CO2 emissions each.
The study appears in the Journal of Geophysical Research.