Dr Simon Boxall, National Oceanography Centre, University of Southampton, said:

"The paper is sound and is the first real evidence of a subsurface presence of oil – I hesitate to say plume as indeed do the authors. I hope it is correctly interpreted by the media as one can see reports of “35km oil slick lurking at depth waiting to pounce”. The amount of oil down there within this large(ish) plume is at most 600 tonnes (if we assume maximum levels across the whole plume) but more feasibly about 250 tonnes looking at their overall data in the limited time available. This fits in with their proposal that about 5.5 tonnes per day is finding itself into the deep column. It is worth noting that they put this input at about twice that expected from natural seeps, which input microscopic globules of oil into the deep ocean in the Gulf as a background.

"This whole paper is actually an optimistic outlook. Keep in mind that the measurements were taken in June when the flow was at a maximum and that dispersants were (possibly foolishly) being injected into the plume. The volumes are not large and there was evidence of microbial activity, albeit slight, even at these depths – so nature works at all levels. The plume is also limited in size - c. 2x35 km – it sounds huge but in ocean terms is small. At the concentrations observed the dispersion would mean that by now the levels would be much lower and some of the material will have migrated to the surface. This deep plume is still only 0.1% of the oil estimated to have been spilt and far from confirming huge plumes of oil in the deep ocean actually allays such fears."