Global pollution measured by lead in mid-ocean sediments

Abstract

On page 278 of this issue, Veron and colleagues at CNRS and at Bordeaux University report their studies of the difficult, complex matter of lead pollution in the uppermost layers of outer deep-water sediments in the North Atlantic Ocean. It is common knowledge that heavy-metal pollution prevails within near-shore ocean sediments, and it might therefore be thought that either positive or conclusive negative evidence for lead pollution in the open oceans should also be readily found in pelagic sediments. But this is not the case: the processes that yield the pollution effects easily observable in coastal sediments also limit these effects from extending into the open oceans. Furthermore, mass-sedimentation rates in deep waters far from shore are so slight that there are serious difficulties in studying the very thin, uppermost, decades-old sediment layers involved, although pollution effects are enhanced by these small sedimentation rates. Such problems made investigators in the past reluctant to search for evidence of lead pollution effects in deep-ocean sediments.